Some advice that NO ONE else is gong to give but in fact isn’t crazy:
I’d suggest every day before shipping out he scream AS HARD AS HE CAN for 10 seconds or more into a towel.
Maybe 50-100 times daily.
Because he will be screaming harder and more than he EVER HAS IN HIS LIFE very many times every single day, and being able to do that super loud will save him LOTS of trouble and exercise.
Here’s another important one:
DO NOT under any circumstances get a Marine tattoo before successfully completing the training.
I’m even pretty iffy about showing up to boot with any Marine swag, short of the haircut, which would show just a little bit that he’s thinking the right way.