I agree completely with the above. Don't waste time in your fabulous, LAST summer off with the boards. You'll discover in your second year that you'll learn almost everything you need to know (and 2nd year stuff is emphasized much more on the boards than 1st year). In addition, most students say that 4-5 weeks of studying right before the boards is all they can handle. Also, 2nd year courses do a lot of review of 1st year stuff--normal physiology, etc. So don't sweat it. The best thing to do is study really hard during the courses...if you do that, you're way ahead of the game.
For my summer between 1st and 2nd years, I managed to find a paid research job that wasn't too time consuming (3 days a week, and not full days) with clinical experience (2 days/wk), worked with department heads (read: recommendation letters from good sources!) and I got a paper out of it. That's going to be a lot more useful for me when residency apps come around than spending extra weeks studying for the boards. Besides, I had FUN. 🙂
Good luck!