So much knowledge can be had on the web, so if I had to narrow it to 3 reference type books...hmmm....
*Definitely a local lore book, plants and such.
The one I have is Edible & Medicinal Plants of the Rockies by Linda Kershaw. There very well could be better but... Good to now what to stay away from and what is safe to wipe your ass with. *Absolutely, a military survival guide. I don't know which branches is the most comprehensive, but i have the Army guide, it has a ton of good information.
James Wesley, Rawles' book How to Survive the End of the World as we Know It is a good read to get your wheels turning and start the process. Most of the information can be retained, not quite reference material. Maybe a good modern primitive medical book, we are a medical family so that is not a priority for us. The Foxfire books are a fun read but not so much guide. They are an old three book series (I think) that chronicle some old hillbilly ways, skinning squirrel, moon shining and such, great stuff. Not to many comprehensive books that cover everything, just have to pick your topics. I also like the old Nuclear War Survival Skills by Cresson h. Kearney
Oh and maybe a Bible
Take Luck