Although it might not be possible for every team member, or every school, I would advise going to the gym for 10-15 minutes before you start during the build season. You don't need to do any major weight, or speed on the treadmill, just something to get your heart rate up and keep you healthy.
Our school has a weight room right down the hall from where we do most of our work during the season, and for the past two seasons, I have been going down there right after school and running a half mile or so and doing some mild lifting. Nothing very strenuous, just to keep my blood pumping!
Like I said, I understand that some kids cannot do this, but if you can, its only 15 minutes. You can make that up by leaving from dinner early!