Totally depends. Most of the teaching is done via the powerpoints/handouts that the lecturers make up, and the idea is that all the information you need is enclosed in those binders/attachments (depending on how you get them). Some students will also purchase books if they find they learn better out of a textbook with a more narrative style than a bulleted powerpoint (or if they just don't want to deal with lecture and would prefer to learn on their own). Med school is very much styled to let you learn how you want to learn, so if you want to go to lectures or watch the vodcast and learn out of the binders, great, if you want to never open a Brown handout, that's cool too.
First year the books I found particularly useful were the neuro one, Microbiology made Ridiculously Simple, BRS Physiology, Robbins Review of Pathology, and Goljan Rapid Review Pathology.