A large book, sometimes called the PDR that has information on just about any prescription drug you could imagine. It includes such useful things as the name, both generic and brand, the ingredients, the side effects and interactions with other drugs.

Since it is a reference the prose tends to be a bit dense. Probably not a good book to take with you on summer vacation. On second thought, maybe it is. I guess it all depends on what you like to do on vacation.