None of them are must buy. The Library has them all, people in your study group will have them and most if not all test questions come from the notes and lectures. I bought all the books and more that weren't even on the list. At the beginning of my third year, most were still in the wrapping. The ones that I used were netters, the physio book (guyton), robbins path, a board review biochem, a board review neuro anatomy book ( I liked BRS), and most importantly a pocket medical dictionary. The rest were unopened. I used my groups stuff or the library's stuff for everything else. In your second year buy first aid to study for boards. Good Luck.
