I think it depends on what kind of a person you are. I was the type who couldn't really take my mind off of it for that summer, and I found myself talking to whoever I could for scraps of seemingly trivial information. I wanted to know everything, from what cadaver dissection is really like, to student clinical experiences, you name it, I was hungry for information. When I found myself waiting anxiously for school to begin, I did start some reading for anatomy, because I knew that was coming first. I don't know how much it helped me, but I just needed to do it to calm my nerves somewhat, and feel like I was doing something to move forward. If you have relaxation type things that you would like to do, I agree, take your opportunity while you have it. But if you are the type who needs to feel plugged in to medical school now, get yourself a Netter's Anatomy or Physiology Atlas and start reading.
I do have a bit of advice for you about the upcoming year. Buy First Aid For the USMLE Step 1 BEFORE you begin your classes, and use it as a review as you take each course during years one and two. The Board Review Series books (with the checkerboard style covers) are excellent too, and I use those as an extra resource as I take each class. I have step one coming up, and I'm not planning on buying any more books than the ones I mentioned, and I think it's good to review with books you are already comfortable with.
Congratulations on your acceptance and your decision.