Do not buy anything, yet. Each school has different stuff and you will NOT need books for the most part. Some things you will buy, but like I said, subject to which school you attend. It's not necessary. If you really wanted to familiarize yourself with some content prior to first year, I would recommend some of those videos on youtube for the basic sciences like anatomy of the human body, nerves and their innervation of muscles, blood supply and their anatomy. There are a plethora of stuff you could watch on youtube. If you think about it, a lot of the basic biology stuff you learned in biology undergrad is just re-taught but with more of an emphasis on the details and more content.
Don't even bother learning the majority of other content because it is too early. You're going to start with the basics and then build on, so if you REALLY wanted to get ahead, start with the basics.
Although IMO, I'd personally enjoy your free time. It'll be mostly gone when you start so don't take it for granted.