My advice for the summer is do nothing school-like. You will get plenty of this during the year. Just keep in mind that you'll hit the ground running when you start school, and prepare yourself to work hard from the beginning. If you do that, you'll be good to go.
I go to Downstate, so I can tell you that the curriculum is well designed to ease you in to life as a med student. What I mean is that the first block starts off with mostly review (it was review for me, even though I only took basic pre-med requirements) and they quiz you early to make sure you're pacing yourself properly. The first four weeks are like this--you do have to work hard, but it's not intimidating, since you've seen the biology before. The big difference is that you're doing a year's worth of bio in three weeks. (Fourth week is about connective tissue).
So spend the summer doing what you like and enjoy yourself. This is your second to last summer off anyway--make the most if it!
Oh-- in regards to anatomy--I bought Gray's Anatomy a couple years ago, you know, to casually read up on the subject because I thought it would be interesting. The thing is, the anatomy course is very specific and focused--you won't be interested in reading Gray's until you have an assignment to work on, because it's just like that. Again, at Downstate they broke us in gradually, like most places we began with the upper limb, which is a good place to start, and there's enough time during the block to adjust to learning anatomy. Personally, I found that without the direction of the course, I could not peruse Gray's Anatomy with any effectiveness. Don't worry about anatomy. Don't be intimidated by this course. 🙂