Just to add on what critter said, there is a strictly enforced dress code in clinics: no jeans, nice tops and if you are wearing scrubs outside the OR, then you must have a lab coat over them. People do wear sneakers, especially in the OR, but they are nice looking ones.
Anyway, as far as going to class, you don't need to worry about buying a new wardrobe. Just wear whatever. I can't think of anyone who wears PJs to class (although there are a couple of people who wear yoga pants or jogging suits), but jeans and a sweatshirt are fine.
I would, however, dress up for orientation (except the day you play in the forest). One of those days you get your picture taken for your ID badge that you will wear in clinics and you don't want to look sloppy on that.