Here's an idea for making an improvised backpack. The basic concept can be improved, depending on what materials are readily available. PVC electrical duct pipe instead of sticks would be lighter and could also contain some tinder dry for fire starting. For the bag, there are many options...carpet; light PVC linoleum, shade cloth, car seat covers etc. The pack frame would be more comfortable if some kind of cushioning was provided at the points of contact with the back. Via:Creative Improvised Backpack - AllOutdoor.com
Another idea for an improvised backpack.... Via: Backpack | Five Gallon Ideas A bucket with a sealable lid would keep the contents dry and also work as an improvised flotation device.
That's a rather super idea, especially if the bucket is filled with "bags of bags" for each type of gear. The bucket would make a fine seat by the campfire, which is often no small luxury. And a small pillow strategically placed to make it easy on the back is also good, too. Just paint it camo, and it's good to go. I wonder how much it weighs compared to a Medium Alice & Frame? It would be easy to put a belly band around it for outside pouches & pockets in any desired array. Hmmmmm.
With the lid, it would be water tight, but it would still need a frame for long treks or for gear like sleeping bag and tents.