After 3 years of college my son has only had to buy 1 book from the bookstore. He has purchased all the rest from Amazon and has not had any problems. Then he sells the ones he doesn't want to keep on Craigslist. It has saved us a lot of money! My daughter starts college this fall and we will do the same thing for her - as soon as they post which books she needs.
We bought his sheets & things like that from Overstock.com.
Good luck!