I'm sure that you're recruiter will be filling you in on all that you need to know, but as a recruiter myself, here's my 2 cents:
The Sailor's Creed, 11 General Orders, and Rank/Recognition are the three most important things to learn
first, in that order. And learn them as soon as you can. If you think you can put it off and learn it last minute, you'll learn the hard way that you can't. If you aren't a very good runner, start now. Technically, all PT is voluntary and the recruiters can't
make you PT with them, but take advantage of the opportunities and do it voluntarily. If you can learn all the stuff in your DEP book and are able to do the push-ups, sit-ups and the run, boot camp will be a breeze. The sooner you're able to do all that, the more deeply it will be ingrained in your brain before you ship out, and the better off you'll be.