I’ve been using the REI Ruckpack 28 the past ten months to haul my 15” MacBook. The zippered side pocket is where I keep my USB charging brick, pens, and receipts. The opposite side, on the outside, holds my Grayl water bottle. The bottom of the backpack has a separate zippered, isolated compartment for a rain cover which shares space with the main compartment. It’s nice for stuffing in dirty laundry, at most a days worth. There's also elastic bands you can use to hold a sweater on the outside.

The backpack is small enough (when fully loaded) to fit under an economy seat (including prop planes, CRJ types) provided you remove the water bottle out and the seat in front doesn’t have a power unit taking up space below. I haven't had a seat I couldn't stuff this backpack under. It should be able to take larger laptops, obviously that'll cut down on how much room you have for other items. I believe the heaviest I've had this backpack was about 25-30 lbs when it was full of drone batteries and my laptop.

The two drawbacks with the Ruckpack are the lock placement and a lack of larger outside compartment to stuff papers into. The zippers for the main compartment have loops for a TSA lock but the side access is not double zipped, which means you'll have to loop a cable lock through the zipper to one of the carabiner loops to secure (albeit not particularly well).

So far, I've been happy. The threads and zippers have held, it's compact, relatively comfortable to walk around with, and not too expensive. It's been my go-to for all 1-3 night trips or when I have checked luggage (always carry a change of clothes and toiletry).