Peanut butter and banana sandwiches have most of what you need... rice is always a good idea, as it has plenty of starch and loads of protein as well. If you can grab some granola I'd load up on as much of it as you can get your hands on. But yeah the water being scarce thing is the scary part... that eliminates lots of options you could have otherwise used to make some really good stuff.

You definitely need to let us know how you end up making it work. I'll be excited to see how it's done!