We don't have a bookstore in Worcester, but you can always go to the Boston campus to buy any apparels. I believe there is a website to buy some of those things, but I don't know what it is. You can ask around when you get here, or maybe someone else on SDN can shed the light?!
For worcester, several student organizations will sell tshirts, polo shirts, sweatshirts outside your classrooms... usually for a week or so during fall ... so don't worry, they will be making announcements in class if that happens, or you can just see them sitting there with tons of apparels for you to choose from!..
I get my books at amazon.com or half.com, I don't do barnes and noble.. I don't know if they have better prices... or best yet, I buy the books from upperclassmen (hint hint!!) those are usually cheapest, if not, they should be comparable to amazon or half.com prices and you save on shipping time and the uncertainty of getting ur books in a bad condition...