Although not completely finished, I have to share these now, since we are already packing and doing and running around for last minute details. I plan to hand finish them on the plane, imagine that :))
The inside detail was the idea of my little boy, who was already forming the shape and utility in his head loooong before the squares were even something together. He was just remarking that a backpack-with-something-to-hang-things-from-inside is much more handier that one with nothing in it. So I added the loop, and a small pocket, just in case.