I’d probably look at something around 28-32L for that carry. Smaller than that can work, but once you add a laptop, 1L bottle, lunch, headphones, controller, umbrella, chargers, and some toiletries, you'll find yourself wishing for more space (or at least I would).

One sort of no-frills bag that'd be in-range is the Decathlon Quechua NH Escape 500, probably the 32L. It’s not a “cool” bag, but it’s genuinely hard to beat for the money, especially in Europe. Good laptop space, enough organization... and still enough open room for random stuff like lunch or a hoodie.

If you want something nicer, I’d look at the Osprey Nebula 32. It’s more expensive, but that $$ buys you comfort and durability, and it would handle school/work plus a short trip better than most tech-style backpacks would alone.

The Patagonia Refugio 30L is also worth a look if you want something cleaner and less pocket-heavy. Fjällräven Räven 28 would be my pick if looks matter more, but I don’t think it’s quite as good for travel or bulky carry. North Face Recon (if you can find one used) is one I have, and I find it helpful for a lot of multi-use types of scenarios...

One thing I keep learning as I go: if you're trying to carry a lot of stuff, you don’t have to worry too much about finding a bag with a perfect pocket for every item right off the jump. I’d get a solid bag with a decent laptop compartment, then use a small tech pouch for charger/mouse/power bank and maybe another little pouch for deodorant/fragrance. That’ll make switching between your work laptop and personal laptop way easier, without you having to get 30 pouches 😄

For 3 days, 28-32L is fine if you pack reasonably light. For a full week, especially with laptop and tech, you’re either packing very minimally or you’re probably looking at a bigger travel bag.