D.H.
Have you thought about a roll bag? They make bags, like you would take to a gym, but they are bigger and on rollers? They hold alot.............
I don't know if they would be too big, but you can smush them down and such..........some of them allow you to strap other bags on them too....like your backpacks.....
When you had the kids, I found it easier to just buy a new box of diapers, or grab some once we got there when we bought food............that way I was hauling so much up and used most of what I needed before I came back....it might be allittle more expensive at times, but over all the cost worked out most of the time.......some high, some lower.......just a thought......
Good luck and take care......