Bookride compiles a list of "Backpacker Classics": those books which find their way to the top of the pack, where they can be quickly retrieved for the purposes of edification, staving off boredom and impressing that cute blond wearing glasses and woolen socks (which are almost certainly hiding the fact that she left her razor stateside).
My backpack is over 20 years old, and nearly as good as new because I didn't use it all that often. However, at one time or another it did provide shelter for Gravity's Rainbow, Perfume and Lonesome Dove. That's about it, really.
My wife, on the other hand, continues to load her backpack for exotic locales. The works of Tony Parsons have kept her pleasant company, and for backpackers heading out to Africa she recommends Acts of Faith by Philip Caputo (A).
And your backpack?