what would be best to buy at GNC?

I've tried the vitamin pills from wal-mart, but they don't seem to make much of a difference in my workout and sparring. I'm looking to go to GNC this weekend and buy something that will help my stamina when training, sparring and especially fighting. I would go and ask the employee but the majority or the employees just know about muscle improving products , and I'm looking for something to increase my endurance and stamina because stamina doesn't come natural with me like other people.
thanks in advance. Oh, and if its in powder form even better :) i love making those powder milk shakes lol.

http://img.meijer.com/assets/product...0129_A_400.jpg

It'll make you gain weight though (muscle weight).

anything that doesn't make me gain weight though lol

muscle milk sucks. try the rapid drive amino acid powder gnc has. they got one for pre and post workout.

It seems the thing to take is Beetroot, Honest ;D