Baddogg, what position do you play? When I was in highschool I just ate everything in sight because my metabolism was so high. And I'm sure your coaches love to run your ass off like mine did--so I wasn't concerned about getting fat. I think the one thing that will impress most coaches is your work ethic--on and off the field. That means hitting the weightroom hard in the offseason and busting your ass every day in practice. If you work hard, set goals, and don't listening to anyone who may discourage your efforts, you will be able to excel as an athlete. You must have confidence in your abilities. Don't worry about getting a scholarship or going Div.I right now, just take small steps at a time; just try and improve each season. I played for a non-scholarship DII school and that still didn't discourage me. You would be amazed at how many DI caliber athletes are overlooked each year.
As far as supplements are concerned, all I took in H.S. was creatine, protein, and a multivitamin. In regards to training, I think most H.S. coaches are too preoccupied with strength and having their kids lift heavy weights rather than actually putting muscle on their kids. In addition to my strength program I had at school (which sucked) I went to the gym everyday after school and did more of a body building routine. So even though my coaches would get pissed that I wasn't following their program to a "T" (all I did were the squats/cleans/deads/bench) I was still the strongest on the team and I put on about 15-20lbs/year since I came in as a freshman. One word of advice though--BE CAREFUL OF OVERTRAINING--many H.S. kids do this and wonder why they don't make huge gains.
And last--enjoy every moment of your H.S. football career, there will never be anything like it. Once you get to next level, it becomes more of a business and politics get involved--but if you have a passion for the game like I do, that won't make a difference. Good luck in your upcoming season!--kmc