What can I do while I'm waiting for school to start

Start volunteering now!!

Start thinking about cool research papers you would like to write and begin doing some research....at least do some Google searches... that always leads to some interesting information..
Keep a log (or bookmark) all the interesting websites you find.

See if you can find some people or a person who is already doing the job you want to do and see if you can shadow them for a day. That is usually not hard to arrange and most people love to share with others.

See some extra movies and read for fun, because it will be a while before you will be able to do that very much.

Set up routine for yourself to keep up an exercise program and a routine for eating healthy that you can carry through school.

Hey, that's all I can think of for now...enjoy your time off...