I fly fairly often and usually with 4 days worth of kit and I use three tricks combined which works well in any situation.
my backpack is not that important the choice, it happens to be a 40L GoLite Peak with removeable hipbelt so its got cleaner-lines to get through security, aircraft, etc with less to catch and less to lose. I've used for trips to Panama, Trinidad changing via Houston. I lost the chest brace clip silly fool me in Trinidad.
So I also never check luggage, EVER, lots of reasons, wasting time at dropoff, pickup, chance of lost luggage plus I sometimes change my flight, in my last flight back from Panama and from Trinidad I managed to get a seat on the earlier flight and in one case boarded just as they closed the door. I mention because....
Even though there are airline rules on max bag size, if you happen to be one of the last to board, either being standby or late connection or no-status and seat near front of aircraft, etc, all the other passengers will be doing same as you and will have max luggage carry-on and overhead bins stuffed, so....
In the top of my 40L backpack I have a light small 20L daysack, plenty of makes exist, such as from Golite, I remove this and it contains what I'll need during the flight and goes under the seat, that then halves the contents of the 40L pack, which being frameless then folds in half and will fit in any irregular spare space overhead, and you don't have to check it. Inside at the bottom of the 40L pack I have a drybag which contains the rest of my kit.
Some aircraft have some very odd shaped bins, so a soft backpack can squish to shape and take spaces many passengers can't use. So I don't compress my gear very tight as it then makes it a firm shape and harder to shape to whatever space is available so my drybag is one of those eVent drysacs which only becomes compressed by the presence of kit ontop, otherwise its soft for shaping.
I don't think the specific backpack, daypack or drybag are that critical but you need basically 2 half-size bags inside a full bag trick. I do recommend the eVent base drybags so it can let air out at altitude and not pop!