Congratulations to your son!
First, if you haven't already, and are willing to use Facebook, I suggest you join the parents group there: https://www.facebook.com/groups/MITparents/
There's been a lot of discussion on that site on what to do that first week. Many suggest that you don't worry about shopping as in most cases, the student is not in his/her final room. MIT is very convenient to the T (subway) stop, so as long as you find a hotel close to another T-stop, you should be fine.
A car may be more hassle than it's worth but I'll let others chime in. We took a car up to take son's stuff up from home. But once we were up in Cambridge, we did not use it. Then again, we didn't see him much once we dropped him off at the dorm.