Quite by accident I came across an excellent little guide book in my local bookstore. Its a pocket guide to tying fishing knots. It's clear, concise and would fit in a smallish fishing kit like Chris describes on this site. Its on Amazon.com as well.
Title: The Pocket Guide to Fishing Knots
Author: Peter Owen
Publisher: Merlin Unwin Books
Price: A miserly £5.99 / $9.95
Its even bright yellow, so you shouldn't lose it!