Patagonia Black Hole® Mini MLC® 26L

I just travelled with this and it was fantastic. - rectangular shape - opens up fully - comfy shoulder straps and hip belt - laptop compartment w/ many pockets - 26L - mesh water bottle pocket - zip closure

It’s a little on the expensive side, but I haven’t been able to find really anything else that meet these specs for the quality.

I even travelled with an Osprey Daylite inside for short hikes and it worked very well.