We just had a thread on this. Get some salt, some "lite salt", some Maltodextrin, a capsulized powder multi-vitamin (NOW makes one), some BCAA caps, and some whey protein.
Mix the electrolytes in (HCl and KCl) at the same ratio as in Gatorade or Cytomax (about 100mg of each per serving), crack open a multivitamin and dump it in there, dump in 100 grams or so of Maltodextrin, crack open some BCAA caps, add whey protein to the tune of 20 or 30 grams, and then whatever you want to flavour it. I prefer red gatorade powder. Banana could be used in place of the KCl "lite salt."
Thats all any drink is: Electrolytes, Carbs, Protein w/extra BCAAs, Vitamins & Minerals. Its alot cheaper to make it yourself.