Agree with everyone in here --- RELAX and enjoy your time off until school starts. Studying would be wasteful and counter-productive, unless you think you have a major deficiency in a basic science core subject. Most people hate biochem and genetics as an M1 so that might be something to brush up on before classes start.
Outside of having fun and relaxing, you obviously want to take care of all the logistical details such as finding an apartment (roomie?), reliable car, gym membership, etc. I've seen some students spend the summer before med school having TOO much fun and neglecting basic things like securing an apt. lease or moving in right before classes start which is exhausting. I would suggest starting your apt. lease a couple months before school starts so you dont get stressed out with moving in and then having classes begin a few days later. Plus, it will give you time to get used to a new city and seeing what it has to offer. Regardless of what others say, you will have some spare time outside of school so you might as well enjoy the local area that you will be living in for the next 2-4 years.