Many students are faced with long summer reading lists with assignments to keep them busy over the extended vacation. This feels like torture but you will see the benefits when you start again in the fall. Your mental processing will be at a higher level and the sudden change back to school life will not be as traumatic.
For those without mandatory assignments, reading as much as possible has always been great advice to keep up your skills over the summer.
While it is advisable to target books that are challenging and related to your classes; even reading lightweight beach books can help keep your mind in a higher gear.
So, grab a handful of interesting books and get reading. Get a book club together with your friends and share your insights (and share your books!). Make a point to read the book before you go to the summer blockbuster movie.
Get your brains moving now and return to school will be a gentle ramp up.