Magic Books
Magic books are how-to guides and step by step instructions for mastering either the basics of sleight of hand, or the particulars of certain tricks. The books almost always feature detailed descriptions, and suggested babble. Babble is the talking portion of a trick, and is key in misdirecting the audience. If you say your actions mean one thing, and the actions seem to correlate then your audience will believe that is what those actions mean.
Magic books will also often provide pictures accompanying most of the tricks. These pictures are invaluable in understanding the movements involved, and many tricks would be impossible to learn without the visual aid.
One major drawback of magic books is that they do not compare well to other methods of learning a trick. The hands down best way to learn a trick is from someone who can do it already. They can walk you through the motions, point out weaknesses in your presentation, and help you personalize the trick. Failing that, videos and software offer a more visually available format for learning a trick than a book can. However for those who want something to read on a trip the book can be irreplaceable.