Aluminum foil to get safe water
If you are out there in the wilderness and you find a stream of water (which is one of the first things that you should look for - very important) don't drink the water raw. It may very well contain bacteria that would give you terrible and painful diseases.
So you must sanitize the water. You can boil it, and unless you want to lug around a heavy pot, you should always have some aluminum foil in a survival kit to mold into a pot (and yes, you can boil water in foil).
You could also use iodine tablets to sanitize the water. You can get them at your local sporting goods store for $5.00.