.. How do I remember all the stuff in these books?

Well, first off, take every book you can. Your inventory is unlimited, so you can carry them all with you.

However, Nancy won't take all of them; for example, she won't take the hieroglyphics book in her trunk, which seems shortsighted to me. In that case, use Nancy's cellphone camera to take a picture of the text. It's a lot easier than remembering which book of the six you've seen has the information you need.