Physicians Desk Reference the most recent edition I could find. This book tells you basically what EVERYTHING you might find in your local pharmacy is, what it does, what the side effects are, and what other drug interactions you could have. If you have the most recent version, you basically have a copy of the package insert for EVERY drug available. It's especially useful if you have some more advanced medical training.
Shiv:
Sun Tzu's Art of War.
I would suggest something more contemporary. US Army Special Forces Field Manual and a Sappers's Manual. Sun Tzu is a little too.... cryptic for most people who need to know how to stage a proper ambush NOW.
Technical manuals concerning the Infantry Weapons used by the country that you live in might also be useful. It would be handy to know, for example, how to operate, maintain, mount and unmount that .50BMG machinegun that you find on the back of that destroyed tank.
This message was last edited by the user at 16:22, Wed 16 Apr 2014.