A news site had another of those "post-apocalyptic library" articles, with guest celebrities picking the five books they'd need to restart civilization. As usual, most of them were useless.
1) Machiavelli: The Prince (who need to do it to)
2) Sun Tzu: The Art of War (how to do it)
3) Marks' Mechanical Engineer's Handbook (how to make the tools to do it with)
4) Merck's Manual of Diagnosis and Therapy (picking up the pieces)
5) something useful for agriculture and food storage, both vitally important to emerging societies, but I don't have a single specific title yet
Unless you can feed yourself, control disease, and defend yourself from your enemies, I don't figure you have much use for classical literature, pornography, popular fiction, or religious works, which are the usual choices.