A search of this forum should turn up much discussion on this. If you need some good references:

Surviving a Wilderness Emergency

98.6 Keep Your Ass Alive

Boy Scout Wilderness Survival Merit Badge Pamphlet

These are all excellent references for survival. The Boy Scout pamphlet is an excellent way to learn about it and prepare. It works for anyone that is not behind enemy lines trying to evade.

Peter Kummerfeldt's and Cody Lundin's books are (or used to be) on the ETS home page as well. These links are to Amazon. They both agree with each other completely except on which chemical is best for purifying water, one prefers iodine and the other chlorine.