By the end of your second year, you should have read these books at least once:
First Aid: just go ahead and buy it now
Pathology: Robbin's Basic Pathology 7th edition, BRS Pathology, Robbin's Review of Pathology
Microbiology: the micro section in First Aid, Clinical Micro Made Ridiculously Simple, (I can't list a text because I didn't like the one we used)
Pharmacology: the pharm section of First Aid, Lippincott's Pharmacology, (I didn't buy the text for this one because our course syllabus was actually decent)
Behavioral: BRS Behavioral Science, BRS Behavioral Science, BRS Behavioral Science. Who needs a textbook when you have a review book that covers everything you need to know for the shelf and the step, and pretty much the whole course?
Of course, different schools have different courses with different expectations. The books I listed are all review texts and are good for helping you get through your courses, plus prepare for your subject shelf exams and ultimately the step 1. For your own particular school courses, you might need to buy the textbooks required (depending on how the instructors test).