How old are you? Still in highschool? I'm not in the military anymore. I got out a few months ago.
Work on your side stroke because you will be swimming a lot. Side stroke, running, push ups, pull ups, mountain climbers, 8 count body builders... stuff like that. you wont be doing any weights stuff till maybe second phase (if you make it that far) and your class works out at the "body shop" (its a lot of machines and stuff done circuit style)
You should talk to you local recruiter station and they should be able to get you in touch with your local "Dive Motivator." He should be holding workouts and getting guys prepped for boot camp. I'm sure you could talk to them and get involved (if its close enough) cause that will help you with your combat side stroke form. you're going to want your form to be smooth when you're doing a two mile ocean swim. That shit sucks and you dont want to be muscling you way through the water.