re: Best Supplement: HS football player

Weight gainer

Whey and amino acids for post workout

Creatine and caffeine for pre-workout (if creatine is still allowed)

Casein or at least 2% milk for a late night snack

Lots of simple carbs around his workouts (e.g. fruits), lots of complex carbs at each meal (e.g. leafy greens, whole grains), lots of chicken, fish, lean beef, and beans.

Almonds or cashews to snack on during the day.

A kid in high school trying to gain weight will probably have to consume a shitload of food. I was 6'2" 195lbs and ate like it was my job. Of course, I ate like shite, but that's not the point. I'd say probably over 3000 calories a day at least, but that's just a guess.