I'm not 100% certain on this one, but I was told in the military that squeezing a lime into a bottle of water, or cutting apple juice like 75% with water is roughly the equivalent of a sports drink if your dehydrated and need nutrients. I imagine it was more of a wilderness last ditch thing, but hey, its natural and cheap.
I'd also like to throw out that a decent post work 4:1 carb protein drink is ovaltine with milk.
I went to the health food store and bought unflavored whey protein powder & a carb powder, I mix it with water and add a little salt and some unfrozened pink lemonade. All natural and tastes fine. You can add some electrolyte tablets but I think it's a waste. You lose sodium but you don't lose potassium on a ride.
I also carry some chocolate milk. I freeze it and then it lasts for hours in 100 degree heat.