to be honest, you really don't need to buy any books because, i believe its two copies of required books are kept on reserve in the library. Most of what is tested/needs to be learned is covered in class and if you want to reference a textbook you can always take it out in the library (for 3 hours at a time).....of course with this you run the risk of the book being used by someone else.
-you will DEFINITELY need the dissector for anatomy lab...it will be ur guideline for dissecting and bolded terms are fair game for anatomy exams. -Some also benefited from anatomy atlases, altho that depends on how you learn...for me personally i never had one and didn't need it because I studied soo much from the bodies in lab.
-For anatomy lecture I used gray's and i loved this book...although you don't need need it, and at times that book can be in more depth than necessary, I used it a bunch of times and would recommend it.
-Bates is also good to have...altho I do know people who never bought bates and just sometimes borrowed others to read assignments for DPR. Quiz questions for DPR and sometimes test questions generally come from there, but they also may come from lecture notes.
-An osteopathic approach to diagnosis and treatment...this book was really good to have at the beginning of OMM...but by the end I hardly used it. The best study guides for OMM quizzes/tests are the videos online and the power points.
when it comes down to it....some people learn really well from textbooks, others do not. I was happy with my decision to buy some books, but it all depends on the person. also, some people may be weak in certain subjects and want to buy the book in that area. i personally would recommend buying the bare minimum of books until you are certain you really will need/use it. It sucks when you pay a lot for a book and then hardly use it. Books can be a great resource if they fit with your learning style..and remember you can always use them in the library if need be! Also remember that whoever you ask will have a different opinion so just try and figure out what works for you..whether that be 1 book or 100 books.
Hope this helps!