I think morals/ethics are ingrained into our instincts, so no need to waste a book on that. As for politics in the free world, each of us should have enough information in our memories to set a good ground work to build a political structure upon, so no need for that. We would DEFINITELY need a comprehensive chemistry book, because there is just too much utility with chemistry. Since this is a physics forum, most of us might be able to forgo bringing a physics or math book. Granted, much will be lost, but there should be enough knowledge to lay a foundation for many things to be rediscovered.
We would want some book detailing biology, especially edible plants and the basics of the biological sciences. Again, we'd need a groundwork from which other things could be rediscovered. I would presume the future society knows how to survive to a degree, so perhaps it can focus more on the theoretical aspects of biology. In fact, maybe a medicine-based biology book would be better.
Finally, a book that details the history of technology or gives a survey of technology, but written for experts so that there is enough detail to give hints on how to rediscover much of it. I don't know if such a book exists, but it would be very useful. Something that covers the basics of mass farming to the basics of machinery to the basics of computers. An engineering book perhaps, but one that touches on everything.That's my take. No need for religion, ethics or politics, since basic human instinct and reason can recreate much of that much faster than it can technological achievements.
, I was thinking of something like a physicians handbook, or some bible of pharmaceuticals and their use. But then a good book on classical dynamics would be useful, as would a book on materials science.