"Harbinger" by Jonathan Cahn. I think I've bumped the book before. It's definitely not about prepping, but a good catalyst for it and a good representation of the times we live in.
Aside from that probably one of my favorites was Chuck Yeager's autobiography. I used to read a lot more when I was younger. I dug through every "Star Wars" book in publication when I was about 14. Some C.S. Lewis, enjoyed Charles Dickens "Great Expectation," but my favorite was Jack London's "White Fang" among the classics.
Obviously though my absolute favorite, and one that belongs in my BOB, is my Bible.
Not sure how much Darwin's "Origin of Species" would help me out when the shit starts flying in all directions.
Correction. I could use it (Darwin's book) for fire starter.