Small, but thorough Survival Book for hiking bag...

[CaptInsano]

SAS all the way.

 

[KiljoyKutlery]

I'd second the vote for the mini SAS guide, I have the full size version and it's a great book.
Being realistic, most survival scenario's last up to 3 days, by which time you are found either dead or alive, so it is unlikely that you are going to need info on wild edibles or die from not being able to tie a riggers bend.
Knowledge of first aid could be a major asset as could be the the ability to make a fire ,build a shelter, signal for help and navigate.

Pit,
Thats funny, all I carry with me is a book on wild edibles. I believe that most if not all of us can build a shelter, start a fire and trap without a book to aid us..but plants can be tricky. And as for first-aid, if you arent practicing, taking a course, or studying a book...you should. IMO it should be required that everyone learns advanced first aid in school, and passes the course.
The big point is that I try to put as much info on everything in my skull, so that when confronted with some type of problem, its easier to deal with.