I have about 1000 flashcards (literally)... I separated them by chapter of the Kaplan book, and wrote concepts or review questions on one side and the answer on the other. This is only for bio, I haven't decided if I'm going to use flashcards for Chem yet. I find them really helpful though, and I separated by chapter so I can take a few "chapters" of questions on the subway with me each day... easier than carrying around a huge book!