I'd really not recommend studying lol. Enjoy your summer and do some volunteering. I tried to study over the summer prior to BMS, it didn't help me at all. The material you'll be seeing in BMS isn't like basic physics, or chemistry material. You are gonna get hit with a lot of different scientific procedures (like PCR and blotting and stuff), some basic biochemical pathways (glycolysis and such), and a bunch of different cellular transporters (Na/K atpase, AE1...). It's all stuff you just have to memorize.
As many people have said in the past, medical school material is not hard, it's just the immense amount of material that makes it hard.