I've hesitated doing a list like this, because I'm terrible at them. Picking just five books to be stranded with on a desert island is as bizarre a hypothetical as it is common. When you boil it down, it's essentially My Five Favorite Books. Except, it isn't.
Assuming I can really take 6 (in order to exclude the Bible) and neglecting the requisite "smart" choice of How to Survive on a Desert Island, here are the five books I'd take with me:
1. The Lord of the Rings by J.R.R. Tolkien
2. John Calvin's Complete Commentaries on the Bible
(I'm going to list this multi-volume set as one book. Because I can. This will likely be the cause of sinking the boat anyway.)
3. The Pleasures of God by John Piper
4. The Confessions of St. Augustine
5. C.S. Lewis's Space Trilogy
How 'bout you? Deserted island. Five books. Bible's a given. Blah blah blah.