Free E-Books
Wilderness Survival
This is the US Airforce SERE Manual, it covers a variety of topics mostly dealing with wilderness survival, and has better illustration than most other military survival manuals
US Military Survival Manual
This is the PDF Version of the Survival Manual FM 21-76 Used by the US military, it's not perfect but it does have a lot of good information. An older version of this book was given to me when I was a kid by my father, and it's what originally started my interest in survival.
First Aid
US Military First Aid Manual
This is the PDF Version of the First Aid Manual FM 21-11 Used by the US military.
Where There Is no Doctor - David Werner
This is one of the best books for medical treatment especially for austere conditions.
US Airforce - Survival Evasion Resistance and Escape (SERE) Manual
Foraging
Wild Edibles of Missouri
The book is a little old and the illustrations can make positive identification more challenging, but it still contains a lot of valuable information.