This lets you maximize storage on the cheap “1x carry-on, 1x personal item” plane tickets. No checked luggage; the 45L backpack just goes under the seat in front of you.
Osprey also makes a good one. Sometimes I need to check something bigger especially if I have a long walk planned but I usually use an Osprey Porter 40Lish (may be a newer line I haven't tried). Yep. Big compartment and use some organizing cubes/bags.