Don't buy a book and toss it into your bug out bag. Practice, practice, practice.
A good book on general wilderness survival is Tom Browns Guide to Wilderness Survival.
Primitive trapping and track ID is covered along with a multitude of other skills.
Keep in mind that these are skills and need to be delevoped in ideal conditions first. The last thing you want in a SHTF situation is a how-to book and no basic working knowledge to go along with it. There is also a magazine called Fur-Fish and Game, lots of articles written by the guys with experience.