Brief Backpack Selection Discussion

I'm just a shade over 5'6", and I have never had a problem with 21" or 22" bags being too long. I started out doing carry-on only in 2000 with a RS Convertible bag that is probablly 21" long. (In fact I used that bag again in 2013 because my partner was using my lighter OPEC bag.) About 10 years ago, I switched to a slightly smaller, lighter OPEC (Outdoor Products, now Campmor, Essential Carry-on). That bag is still 19" long. I've looked and looked for shorter bags, but it seems that as soon as you get shorter than 18", manufacturer think you want a school backpack, and those are hard to pack. I want a bag around 1800 cu in that opens like a book. The closest thing I've found is the Goodhope bag on Amazon. At 1400 cu in, I've fit everything I normally take to Europe in it, but there is no extra room.

To paraphrase the real estate axiom, for me, the three most important features in a bag are light weight, light weight, and light weight. The Essential Carry-on weighs 1 lb, 13 oz. I don't need structure. I don't carry books or bottles, just my clothes; my small netbook goes its own purse size case as a personal item. I long ago learned to parcel the contents for organization. Shirts go in a Tide wash bag, underwear in a RS mesh bag, batteries and chargers in a nylon stuff bag. Packing cubes are way too big for me.

Since I can't find a non-backpack style bag small enough for me, I solved the sag problem by getting an eTech 2.0 Weekender Convertible Junior, with cinch straps, to tighten the load.

Torso length and pack structure/suspension apply to backpacks that have load carrying hip belts. See REI advice for pack fitting: https://www.rei.com/learn/expert-advice/backpacks-adjusting-fit.html

If you are carrying tourist luggage type carry-on packs with under 10 kg of load for short distances, the suspension system and size is less critical than if you are carrying 20 or 25% of body weight loads long distances. If you are carrying heavy loads, then having a suspension system that effectively transfers the pack load to your hips will save your shoulders.

Whenever Lee explains his system it catches my eye because I also aspire to that kind of minimal load, but I always end up giving in to the temptation to add dress items like a blazer and corduroys to my pack --

for the last year or a little more already, I've been using the RS convertible carry-on with a packing folder, a medium packing cube, a ripstop nylon cables/charger pouch, and the RS civita shoulder bag as my personal item (kept inside the pack on travel days and used alone on days in one location). Maybe a small cube, too, depending on whether I don't want to do laundry.

With all that, my RS convertible carry-on still has to be cinched about as far as the cinch straps will cinch, and I also stick in the day's healthy snacks and a hat. The bag has a Swiss Army Knife jack-of-all-trades-but-master-of-none quality that makes it handy in almost every situation, but perfect in almost none. And that's ok for those of us who aren't out traveling most of the year!

My speculation is that if you're traveling as a couple, each person shouldn't need his/her own carry-on and personal day-bag; two people should be able to hold all their things in 3 items, not 4.

@Sun-Baked in Florida

I must disagree with your assessment.

I'm 5'4" and have never had problems carrying a 21" pack. I don't need a hip belt because I pack lightly.

Structured bags are for heavy loads. You shouldn't get this type of load if you pack lightly. The 7-8 kg limit is reasonable for any season.
Please remember that the structured packs are heavy packs. You're actually creating the problem that requires structured packs by carrying a structured pack!

I should also note that knowing how to pack your bag is a bit of an art form. For example, how many people put the fleece against the back of the back so that it protects your back against pokes (not a problem if you are wearing said fleece)? The same goes for knowing how to pack items against shifting etc. Don't let heavy equipment substitute for proper knowledge and training!

I'm kind of a luggage freak, and am in the process of switching over to international carryon size bags. I've ordered the RS wheeled bag based on all the reviews and raves here and elsewhere, but also decided to buy a carryon size backpack for times when I don't want to use a wheeled bag. Although the RS convertible got some really good reviews, I decided to go with the Osprey Porter 30L backpack. It's a comparable price at $100, and is quite lightweight, a feature I really need.

I'm really looking forward to taking this bag on a trip. I've done a practice load, and the bag can really hold a ton of stuff--which I'm going to have to discipline myself to control, if for no other reason, to avoid back strain. It also has a sleek, streamlined appearance as compared to the boxy RS convertible. My goal is to have a bag that will both go in the overhead as well as under the seat in front of me (which will, of course require a less than full packing load. So we'll see!

Some of the aspects the OP mentions are more relevant to hiking backpacks than carry-on luggage. I'm only 5'1" but my preferred bag is this convertible one from Antler. It has served me well on and off trains and buses and hotel stairs, but I am glad of the wheels if I have to walk any distance. I wouldn't take it hiking. Samsonite now do one similar and slightly lighter but only in black.