Not sure what the terrain or temperatures will be for your quest, but if you are allowed to build a fire, I would have to go with a the large Victorinox Swiss Army knife that has a saw blade and a magnifying glass. I would also bring a large dark colored cotton button shirt to erect a sun shade with. You could cut some long thin sticks with the saw, lash them together in a dome shape with your bootlace ends and cover with the shirt. Use the magnifying glass to build a campfire and boil drinking water in your unlined, unpainted, stainless steel bottle.