The items going on this trip happen to be pre-packaged and fairly shelf-stable, at least for the duration of the trip -- but I completely understand about the sandwich problem. I found a plastic container at the dollar store that I thought would work, but it's not large enough and yet too large at the same time. For the time being I'm just going to pack them on top and eat the most fragile items first. I may also stuff a bit of cardboard down in my food bag to act as a sort of shield against getting too crushed. There are enough trash cans along the way that I shouldn't have to carry it more than a day or so.
"Stand in the ways and see, and ask for the old paths, where the good way is, and walk in it; then you will find rest for your souls."