I am near the finish of my Transitional Year. If I were starting intern year again, I would enjoy my summer and spend as much time with friends and family as possible. Your free time will greatly diminish with the start of intern year. You could always buy a high-yield book such as Internal Medicine On-call or On-Call Principles and protocols these are one or the other good books to have on hand while on call. But in no way would I study before intern year. I would just buy a book to have a little security. Uptodate.com is a great resource if you feel like you do not remember much (this is how I felt). When you have a patient that you have no idea what to do you can just read briefly (I stress briefly) and talk to your senior and attending that is what they are there for. I would get a resource for meds such as epocrates, etc. Other than basically getting your white coat ready to start the wards, I personally would not prepare more than that except to enjoy your time off!