Aside from the PT itself, being fit will help you focus better when you are worn into the ground. Basic was one of the few times having recurring occasional insomnia was helpful, as I was used to being up for several days at a time and still carrying on.
Basic is more mental than physical, but if you show up in crap shape, the physical part is harder than it needs to be so that piles on unnecessary additional mental strain as a result, but it's mostly long haul work than short, high intensity activity (think tough mudder vs american football)
Run yourself hard, stay positive, don't quit and remember it's all a game to test your ability to deal with stress, and life is good. 12 years later I still run into wingers from then and it's one of those weird bonding experiences that stays with you, and tend to pick up where you left of after a 5 year+ gap.