I think most people would be best served packing light, and using a carry on size “travel pack” which is a cross between a backpack and soft-side luggage.  Travel packs will often have light weight internal frames to make them easier to carry, handles on the top and side to carry as luggage, and backpack straps and maybe a waist strap that tuck away in case you need to check the bag through. If you have no plans to check your bag, a classic daypack can function beautifully as a “travel” pack.

Most travel packs are really designed for urban use with an emphasis on ease of use / access rather than multi-hour carry comfort. Travel packs address keeping the contents organized, easily accessible, and have clean lines so they don’t get hung up on things. I find I can carry most travel packs <10 lbs for an extended time and between 10-20 lbs for an hour or so. Most don’t have good carry systems and become bothersome for longer duration walks. If you are planning to be walking long distances with your pack, you would be better served by using either a trekking pack if your days end in a town, or a wilderness backpack.

Make sure the travel pack you are considering is still under the limit for carry-ons! Feature and size creep has resulting in many travel packs which are heavy and are too big to be used for carry-on. At the same time the airlines have been reducing the size/weight limits of carry on bags. A caveat is you don’t necessarily want a “max-size” carry-on bag.

A generalization of Parkinson’s law is that the demand on a resource expands to match the supply of the resource if the price is zero. When it comes to luggage it means that you will have a tendency to fill your bag. I mention this because when people start traveling light they often look for a bag that is a “max size” carry-on. This will often lead them to over pack.

Even experienced travelers are susceptible to over packing. Over the last fifty years I have taken trips to the same destination which were of identical duration with the same expected conditions. I generally used whatever was my “standard” bag of the time which has ranged ~15L-46L. Each trip generally filled the bag with things that I asserted were “needed”. What was the difference? Some of it was experience and more compressible items, but mostly it was the smaller bags forced the question “Is this necessary?” The smaller the bag, the more frequently my answer was “no”.

If you are new to onebagging, I often recommend getting a bag that’s a bit smaller than you think you “need”, because you will discover there are several items which aren’t actually needed. I can’t remember ever regretted carrying a smaller bag, never felt like I didn’t bring something that would have enhanced the trip. If anything, the trip was more enjoyable. When I carried the larger bags I sometimes did regret bring as much as I did because items ended up not being used and on long walks the bag felt like a burden.

In my experience, many people will be well served by a bag that is 25-30l with dimensions of 7.8×12.5×20″ or less which virtually every airline permits as carry-on. This size bag might fit under the seat in front if you, though with the smaller seats and intruding infrastructure they sometimes need to go into the overhead storage. There are exceptions to this recommendation. The first are people who are big. For example the clothing of someone who is 7ft tall with size 47 feet will have troubles fitting into a bag that works well for my 5ft wife. The second exception are people who are engaged in special activity which required a lot of gear, or gear which can’t be carry-on and they aren’t going to rent at their destination. Special note to photographers. Do you actually need 2 bodies, 6 lens, numerous filters, 6 batteries, and a pocket camera? If you are doing a wedding the answer could be yes, but often a single body and 1 or 2 lens might actually unlock your creativity and improve your eye. Finally, there are people who are going to be in a location for an extended period and the supplies and items they need for day to day life can’t be acquired locally and won’t fit in a bag which is carry on approved. In some cases the supplies won’t fit into a single check-through bag.

My ideal bag is small enough to fit into a “personal item” sizer for the low cost airlines I fly such as RyanAir 43x25x20cm (16.9x10x7.8in). My bag is technically larger than these dimensions, but so long as it’s not overstuffed, it has be able to squish into the sizer, and I have never been forced to pay the fee for a carry-on bag. This is my primary bag and what I used 95% of the time. I also have a 40l back country backpack when I need to carry heavier loads / more volume. I like keeping things simple. Many people who travel a lot have a number of bags so they can select the bag which meets the exact needs of a trip. Often these people treat their bag collection as a loaning library helping friends and family.

Many airlines used to define carry-on bags as being 45 linear inches which enabled people to bring bags / objects longer than 22″ such as a garment bag or back country backpack. These items often had to go into the overhead bin sidewise which means someone else might not have room for their bag. These days the largest permitted carry on is typically 22x14x9in (55x35x23cm) which perfectly fits most overhead storage areas. It’s possible to overstuff soft side bags to the point that they will not fit, even it the bag is theoretically the “permitted” dimensions. There is a summary of common carry one restrictions, and an exhaustive periodical table of carry on size limitation. When it doubt, check with your carrier. The packhacker site list which airline a bag is guaranteed to qualify as a carry on.

My Choice

I use daypack rather than classic travel packs. When I don’t to need too many “options” from my packing list I use a discontinued variant (my review) of the Gossamer Gear Vagabond Jet. On trips that mix my travel with wilderness backpacking or I need to carry a heavier load extended distances I use a  Hanchor TUFA which was picked up on a whim when in Taipei. If I needed to regularly carrying more than 20 pounds or 40 litters I would pick up a ULA Camino.

“City” Use

Travel packs vary in the amount of “organizational features” they have. One approach is to divide the bag into sections which often directly accessible from the outside of the bag. In theory is it’s quick and easy to retrieve a particular item without disturbed most of the pack’s contents. If the way you separate you items matches the size of these compartments this works quite well. The other extreme is that the bag is just one large space (with maybe a pocket or two for small items). This has the advantage of being very flexible. The downside is that finding things in the one large section can be challenging. People typically manage this by using packing cubes or stuff sacks to collect smaller items together. When using stuff sacks or packing cubes fill them with items you use at the same time / location. For example, if you use a charger next to the bed, group it with other items you use in the bed like sleeping mask rather that with electronic items you use on the go. In between are bags that have external access to compartments, but the divider is light and flexible materials that allows the main compartment to “take back” space not used by the small compartments. I personally tend toward the one big compartment, though my Synik 30 has numerous compartments.

Below are a list of travel packs which I think are worth a closer look. This is list is in roughly in my preferred order when considering function and price. Note: this list is dated. I have been pretty happy with my current bag so I haven’t been looking seriously / trying bags since Jan 2023.

1. Gossamer Gear Vagabond Jet: super minimalist 23L pack with few organizational features, light weight, durable, and carries well. Flat waterproof bottom lets you put it down on the ground and easily access the main compartment. One of the less expensive bags for its level of quality. If you are traveling ultra-light could be a nice option.
2. ULA Camino: A full feature back country backpack which has been designed to be travel friendly. If you are going back and forth between city and back country with a heavy load and need a carry-on sized bag which can expand when on the trail to hold multiple days of food, this is your pack. If I was to buy a larger bag, this is what I would most likely purchase.
3. Osprey Farpoint 40: Less functional volume than some of the maxi-volume carry-on size bags which is offset by a real frame that is comfortable for me up to around 22lb, a large pocket on the opening panel, an externally accessible padded slot for laptop, a number of built in straps to keep everything in place. Downside is no side pockets. If the load is less than 10lbs, I would prefer several of the following packs over the Farpoint, but if the load is a bit heavy, the carry comfort of the Farpoint trumps most of the other packs in this list. I would say that the Farpoint (or women’s Fairview) is the “safest” / most likely to be an effective travel pack the most people, especially for someone who is just starting onebag travel. The daypack can attach to the back or hang on the front from the shoulder straps.
4. Osprey Daylite 26+6 is a popular bag on /r/onebag. If not overpacked will be considered a personal item by many budget airlines. Can be expanded if you need to carry a bit more. A nice set of organizational feature. Reasonably comfortable to carry. Sells out often and then restocks. Can often be found for less than $100.
5. Cabin Zero Military 28L (durable) Classic Tech 28 (lighter more features) are reasonably price personal sized item which is well designed.
6. Decathlon Forclaz Travel 500 Organizer 40l: No personal experience but reported to be quite good, less than $100. Max size carry-on with good organizational features.
7. ULA Dragonfly: For minimalist packers who are dialed in. Small bag, beautifully made, great material, good shoulder straps, clean design. Often out of stock with new packs appearing Wednesday mornings. There is also now a 36l Dragonfly.
8. Patagonia Mini MLC 30: A well designed duffel with comfortable backpack shoulder straps and just the right amount of organizational features. Laptop and “office items” near the back, small organizational out the front of the bag, with a fairly large main compartment. Side water bottle stretch pocket. Grab handles including one that can go over wheeled back handle.
9. Bags from Tom Bihn: All the bags made by Tom Bihn are amazingly well thought out, have great organizational features, and are top quality. Choose the bag that fits your packing need and style, but be prepared to pay for the quality. The downside of Tom Bihn bags is that they don’t have the class leading weight to carry volume nor are they the most comfortable when carrying significant weight for longer durations. If you are carrying a heavy weight, you will likely prefer one of the other travel packs listed that have padded waist straps. We will how TB fares with Tom and his lead designer retiring and the company purchased by a capital management firm.
10. Rick Stevens Back Door Bag: A great value. Typically less than $80. Light weight. All the features that are critical. Not as refined as many of the bags on this list, but also significantly cheaper than most.
11. Cotopaxi Allpa 35l was a Indiegogo funded project but now easily purchased at stores like REI. Well designed bag that unzips suitcase/clamshell style with zippered mesh compartments. Has a fair number of organizational features and externally accessible laptop compartment. Hip belt does an ok job of transferring weight. Wish it had an external pocket to carrying water. This bag calls attention to itself with the bright, multi-color fabrics pieces. I have noticed a lot of shorter women rave about the packs fit and carry comfort.
12. REI 40L Trail and Rucksack 40 are pack which seem well liked by the onebag community and supposedly can transfer significant weight to the hips, is easy to purchase, and reasonably priced. It can stretch to be used in the back country if you are carrying an ultralight load. I have only tried them in the store. I didn’t find them comfortable with >10lb and had trouble getting it into a comfortable position. The zipper configuration that allows it to be partially opened for top loading or fully opened seems nice, but I found the zipper often caught in the transition area.
13. Lowe Alpine Escape FlightPro: 40l. No personal experience, but on paper looks good.
14. Tortugaback Packs is a small company that makes packs specifically designed for the light weight traveler. Suitcase like zipper opening, side access laptop sleeve, zip away straps, and other features make this a well designed travel pack. Waist belt actually transfers weight. Heavy.
15. Matador GlobeRider45: No personal experience. Looks like a very nicely design max size carryon travel pack which should have good load transfer to the hip belt. The one downsize is the pack by itself is more than 4lb.
16. Peak Designs Travel Backpack 45L is a kickstarter project from a company that has delivered numerous successful projects designed for photographers. This bag would be ideal for photographers, and would be a good bag for just about anyone. The back has good access and organizational features, and opens likes a suitcase. The hip belt actually takes some weight off the shoulder making it comfortable carrying moderate loads. It can be slimmed down to 35L by closing two side zippers and snaps (which have a tendency to pop open when pressured). It’s very durable. Heavier that I would like.
17. Opsrey  Porter 46: A durable bag which will protect the contents better than many other bags because there is closed cell foam sewn into the sides which also gives some structure without adding much weight. The “strait-jacket” compression system is very effective but the straps need to be released when you want access to the main body of the pack. They’re a fairly large top pocket which I put everything I might want quick access to while on the move. The lid to the main compartment has an external accessible zippered pocket, and a mesh pocket on the inside. One side of the bag has an internal mesh pocket which runs the length of the bag. This is one of the more comfortable carrying bags I have found though the hip strap is more stability than weight transfer. This pack unfortunately doesn’t have an external water bottle and is a light on organizational features. This was my primary bag for ten years. There is also a 30L version of this pack. Note: Osprey periodically makes minor updates to this bag, at which point you can often find “last year’s model” on sale for less than $100 which is a very good value.
18. Patagonia MLC: Nothing special but nothing particularly wrong either. Decent travel bag with backpack style straps that hide away. I haven’t see the most recent update so might be better than the first version I tried.
19. zPacks Bagger: expensive, light, minimalist pack (doesn’t have a laptop/hydration sleeve). Avail in 25 & 40l. No personal experience other that briefly putting it on my back and walking for a couple of minutes.
20. Patagonia Cragsmith 45l: The foam sewn into the fabric give it a stiffness which provide structure and padding while adding modest weight. Stands up on the bottom with a zip top which provides good access. When laid of it’s front the entire back unzips providing full access to the contents while keep the harness out of the dirt. When empty the foam keeps structure. This bag “natural” size is 23″ x 14″ x 8″ but it will squish into many carry-on sizers provided you don’t overpack. The side pockets are quite tight, your average water bottle will only fit by pressing in against the contents of the pack. The carry comfort is surprisingly good up to around 20lb. They also make a 32l version that has a webbing belt.
21. MEI: One of (if not the first) travel pack makers. Very durable, carries well. Hard to find in local stores… when doing mail order you might need to wait for your bag to be built.
22. Marmot Long Haul, Northface Basecamp Duffel (Small), etc: Very durable and highly water resistant. A good option if you expect your bags to be outdoors a lot and you aren’t looking for organizing features (Marmot has a few features, TNF none). I didn’t find either as comfortable to carry as the Osprey Porter, but would choice it if I expected my bag to spend a lot of time exposed to the elements. Duffles are really nice if you are doing a lot of loading / unloading. Many other outdoor companies make similar duffels with straps which are roughly equivalent: Patagonia, REI, etc. Consider how easily the straps come on and off, and what against your back.
23. Granite Gear Cross Trek2: Moderately priced 36l bag. No personal experience with it, but generally have had good experiences with Granite Gear Packs.
24. Minaal Carry-on is a pricey bag that was a successful kickstarter project. The bag zips open like a classic suitcase for easy access, has an external water bottle pocket, removable straps, and a well designed padded pocket for a laptop. Clear design, but the webbing waist strap is only for stabilization, not load transfer.
25. Nomatic Travel Bag is a kickstarter project bag designed for travel. Well designed with a lot of organizing features. Clamshell opening, shoe compartment, side storage pockets, internal waterproof water bottle pocket. I don’t have personal experience using this bag but it seems well regarded.
26. ULA Atlas: A 40L Travel Pack designed by people who normally do back country backpacks. I have not seen it in person, but likely has a better suspension than most of the other travel packs and lighter weight. Won’t have all the organizational features of some of the fancier travel packs, but for many people that shouldn’t be a problem. Carry-on approved for some airlines, but several limit you to 22″ and the Atlas is 23″.
27. Rangeland New Business Trip Backpack: $45, qualifies as a personal item with most airlines. No personal experience but several people recommended it. 
28. Decathlon Forclaz Travel 100, 40L Hiking Backpack: Inexpensive travel backpack. No experience but worth a look.
29. Decathlon / Quechua 23l NH Escape 500 rolltop: budget bag which qualifies as a personal item.
30. Goruck GR1: I don’t really understand the love as a travel bag, especially given it’s high price. Yes, it’s seriously durable, but short of doing military deployments I don’t believe most people need a pack which is that rugged, and you pay for the weight. The other issue is that I didn’t find the shoulder straps that comfortable when carrying more than 20lb. I will say that no pack I have tried keeps rucking plates in place as well and Goruck packs. A GoRuck lover told me that they need to break in and I didn’t use it long enough to experience it. I have never heard about a backpack that needs to be broken in before.

There are a number of other packs which I don’t have experience with that might be work looking at such as AER, Bellroy, Cabin Zero, and Evergoods. There is a spreadsheet of popular onebags and an analysis of what bags are being used by the /r/onebag community. The packhacker sites has lots of reviews and list which airline a bag is guaranteed to qualify as a carry on. I don’t necessarily agree with how they rank bags but they have an extensive list of bags and details about them.

Packs for Trekking or “Wilderness” Backpacking

If you are planning to be walking long distances with your pack, you would be better served by using either a trekking pack if your days end in a town, or a wilderness backpack.

Remember that you can’t take fuel on a plane… plan to acquire at your destination. You can’t bring knife, stakes, or hiking poles as carry-on. Sounds like there has been clarification so you should be able to take tent poles… I have made it trough 8 TSA / security checkpoints carrying a zpacks carbon fiber tent pole. I have been wondering about taking chop sticks instead of stakes. If you need to carry these things, you can ship them via a postal carrier, send them through as checked baggage (cardboard poster containers work well), or send your backpack as checked luggage. If you are shipping your backpack as luggage I encourage enclosing it in either a duffel bag or cardboard box. Ikea Frakta storage bag /duffel is cheap (<$5), durable, light (6oz) and large enough for most packs. Other hints about flying to reach backpacking destinations.