The Lightweight Manifesto
A lot of people consider Ray Jardine's "Beyond Backpacking" to be the Bible of lightweight backpacking, and in some ways they're right. Jardine's book is the ground text for rucksacking, and many of the innovations he came up with are still the best we've got. But that doesn't mean every word is golden. Have you ever read the section on food? How about Ray's preoccupation with dry socks? Also, the book is long, and life is short.
If we had to choose one prime text for rucksacking, it'd have to be Lightweight Backpacking 101, put together in August of 2001 by the people responsible for Backpacking Light. True to lightweight backpacking form, it's also a lot shorter than Jardine's book, and gets to the essential points quickly.
Lightweight Backpacking 101 [Backpacking Light]