100% agree with gyngyn, especially the point about getting hooked up with your school's resources early. SO many students don't reach out to their school, but most schools have a team of people who are there to help students make the most of their education.
I would add: spend time getting to know how to use Anki.
Also, spend time with family and friends. Get tons of exercise and sleep. Go on a vacation if you're able. All of this shuts down during med school, so the very best prep you can do is charging your batteries as much as you can. Come into med school well-rested and ready to go.
There really is no point in pre-studying, but there could be great benefit in reading a bunch. Think about reading basically anything by Atul Gawande, or books about the social impact of medicine (The Immortal Life of Henrietta Lacks, Black Man in a White Coat, In Shock, This is Going to Hurt). Listen to the first season of Dr. Death podcast. Those types of activities will keep your brain moving and also prepare you for some of the softer skills you'll need in med school.
