a backpack is more convenient to me bec. if it is with wheels it may may cause you inconvenience. You wouldn’t want to get stuck in stairways, the uneven roads, sidewalk or pavements, etc. They can also get in the way when you are taking public transportation...
but you can also with the backpack with wheels
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In my experience, a backpack is way more practial (your hands are free), and you can pack quite a lot of stuff in a 80-90 Liters backpack (if you know how to pack to save space).
For day-trips (e.g. hiking) you'd need a smaller, ca. 30 liters backpack (you can carry it on one shoulder even while carrying the big pack), and you can carry wallet, passport, cellphone, etc. in a small always-on-you bag.
In my opinion, 'a 80-90 l backpack' and 'practical' in one sentence sounds odd... and a 30 l one for day trips?? Last years, I've always travelled with a backpack of 27 l, and that was big enough!
Shameless brand promotion I know, but theres a certain company that sounds a bit like forth race.. that make a Duffel bag with backpack straps that is literally indestructable, the thing is not particularly heavy, totally waterproof and you can attach it to pretty much anything, up to and including a Yak. Ive taken mine Hiking, Camping, on Weekend breaks round Europe, North America, the more Icey bits of Canada etc etc etc and I swear by it!