My tip (I've been flying interstate nearly every week for 25+ years) get a bag with the least amount of extra pockets or zippers as possible.
Backpacks for domestic travel can be a PITA. Keep it simple, you'll only fill the extra pockets up with crap that you carry everywhere and never use. Same with an iPad or laptop bag, less is best.
I've just converted to one of these and have a second one now for swmbo. Duffle bag and shoulder pack in one. We don't use them as a full backpack as pictured, but do on occasion use one shoulder strap in an over shoulder style.
Never had mine full, but can accommodate 1 night to 4 nights away packed clothes.