I contacted my area's NROTC unit when I got picked up to see if I could PT with them every once in a while or at least just do Navy-related activities. They told me that for liability reasons thats not possible. You can however go chat with your NROTC folks, usually pretty good guys with good info. Other than that, I second what Otto said, although its a good idea to not get caught doing anything illegal. I hear they frown upon that these days.
Though for the record they can't drug test while you're in BDCP. I thought that was weird.
That's 100% absolutely false. I did a drug test (maybe two?) while in BDCP. If anyone interpreted what I posted above as seriously advising you to do illegal activities, then you're stupid. BDCP is a great deal. Don't fuck it up. BUT I was simply saying to enjoy all the freedoms you are giving up once you start your Navy career. Growing hair and piercing your ears isn't illegal or prohibited in the program.