I have the already mentioned SAS Survival Guide, Army Ranger handbook, and others in a similar vain. I keep a small version of SAS SG in my Bag of Tricks because, while I spend a great deal of time recreating outdoors, who knows when the one little nugget of info in there might make all the difference when I'm tired, cold, hurt, hungry, dehydrated, and wet. Best case sinerio, I'll use that little book as kindling.
I also think historical books like The Boy Captives and Drums Along the Mohawk are quite valuable because they remind us that what one human can do, so too can another. Never quit, boys and girls. NEVER QUIT! You stay in the fight 'till the fight is taken out of you. And I'm not just talking about physical altercations.