AP Chemistry is not something you would ever want to self-study. Just keep that in mind before reading on. If you are planning on self-studying Chemistry, please don't. There is so much lab work that you need to do, and so many random things that you need to learn for Chem. It's not something you want to try to learn the night before (or review the night before... trust me, I'd know).
If you are really bent on self-studying, you are going to want to buy the Zumdahl Chemistry textbook. Trust me, you will need it.
As far as preparation/review/whatever you are going to want to find a good review book. I bought the Five Steps to a Five AP Chemistry book, the Barron's AP Chemistry book, and the Princeton Review AP Chemistry book, along with a Five Steps to a Five AP Chemistry 500 Questions You Need to Know book. Personally, I really hated Barron's. It gives you so much useless information, and it reads so slow. I felt like I had been reading for a million years after just one chapter, so I would definitely not recommend getting Barron's. The Five Steps to a Five book was on the other side of the spectrum; it didn't have quite enough examples and information. One thing I really liked was the fact that it had very realistic questions though, that's why I bought the 500 Questions You Need to Know, which I would definitely recommend. Finally, the Princeton Review book was pretty shallow as well, but if you have already taken an AP Chem course, you should be fine reviewing with Princeton Review and just refreshing yourself on the stuff you have forgotten.
Quick Tip: You don't get to use a calculator or formula sheet on the multiple choice portion, so don't forget to memorize your formulas and sharpen your mental math skills.