Although most everything you need will be located within walking distance, the occasional need or want to go further out can be satisfied with multiple transportation options. A car, in most cases, is the best means of getting from point A to point B.
The walks to and from class are not that harsh, and may actually help ward off the "Freshman 15," but "the T" is excellent if you would rather not walk. It is as easy as stepping on and sitting-you do not need a card to board. The only situation that creates an absolute necessity for most students is the ability to travel home for breaks.