I'll let somebody else answer the Careers Service question, as its roughly another five years before I'll take any interest in their provisions...
As to good places to shop in Cambridge; Open Air (I think its called) on Green Street is great. They have good staff who will probably give you great advice and product info and help you find boots that fit and stuff. There's a cheaper looking place on Bridge street, but I doubt they'll have that selection.
Millets usually has some very basic stuff, but not much variety. And there's an ok sized Blacks at the Grafton. At least these two do student discount.