i always bought my books early in undergrad from online sources, etc. to get them WAY cheaper. however, when i arrived at med school, the 2nd years told us what we needed, and it turned out i used even less than that. there will be a few books that you definitely use (i.e. anatomy and your clinical skills book), but it's safe to wait for your books, especially since they print out your notes at most schools now.
one person's input.
-Aaron