I'm not a nutritionist, or sports med doctor....

Creatine, make sure your kidney function is fine first.

I tend to agree wtih bentirran. Most of the point of sports drink is to get electrolytes into your body quickly, instead of pure water. As most of us know, overloading on just water can lead to a hyponatremic state, which can kill ("water toxicity"). As long as you take some food, a powerbar, whatever, water is just fine to drink.

From personal experience with my own weight lifting, I've found that if I work out enough that I'm starting to build muscle, I'll crave protein. I've been known to eat a protein bar (one of those 22g Power Bars), 2 eggs, and about 1/2 lbs. of ground beef after a work out. It only happened a few times, but the muscle definetely appeared.

Anecdotally, I knew a few of the football players in high school that used the stuff from GNC, and it seemed to work fine. Muscle building, though, is done through weight resistance, not necessarily aerobic work. So unless you plan on lifting weights in addition to cardio, it'll probably just waste money.