whey protein with carbs, it is a must after workouts.
a good multi vitamin as well. don't go cheep on this one.
If you have extra cash, add creatine to the mix.
I would say some other stuff but beeing 15, I doubt that you would have the money to buy anything else.
I'm not talking shit or anything, it 's just the way it goes sometimes. besides, you have something you can't buy................youth!
KJ