dRelax; if they know he is coming they will make themselves clear as to what they expect and how the program will unfold.
In my mind what is important is "helping" your son get focused with his new life. Make sure he has what he needs to focus on his studies. My standard advice to parents is to go see him after 4-6 weeks, take him and his roommate(s) out to dinner and listen to what they have to say (don't talk, just listen). Listen and learn; you will then be better prepared to help him focus on what is important once he gets to the riggers of baseball.
Baseball is baseball; the coaches will have a program and they will make sure that he knows what they expect. The hardest part of being a freshman is learning to be on their own, managing their time without parental oversight and learning to compete academically at college where educational standards and expectations are higher than when they were in HS.
As to what to bring; they will bring what they think they need for baseball. Until you make the team you are generally using your own "stuff" so plan accordingly.