Skule 20

Fjällräven Skule 20 is my bag for this kind of stuff. Been with me in many countries, and also with budget airlines under the seat. Seems to check all your requirements. Also some good color choices imo.

If you fill the bag up completely, you won't get a water bottle in the side pockets. I hate that, and noticed it with multiple Fjällräven bags in the store. Just no reason to not include decent side pockets, this has been figured out, just go ahead and implement it instead of doing whatever this is.

Great items on Zalando: Fjällräven-SKULE 20 - Hiking backpack - terracotta brown https://www.zalando.fr/fjaellraeven-skule-20-sac-de-randonnee-terracotta-brown-f2554o058-o11.html

I recently bought a Fjällräven Skule 20 for a trip this summer and it became my go to backpack in the city. Not sure if you're from the US and the brand is known there, but it's a Swedish brand that's very well known in Europe. Their most famous backpack is the Kanken model, but I find this one much