As a rule, I would say avoid ANY caffeine at all costs. It's just not natural. Your body doesn't need it.
Some sun-dried bananas (or just normal bananas) are great though. And here's a great sports drink you can make that blows away the expensive commercial ones:
Squeeze 1/2 to 1 full lemon (they are very high in minerals). Add an equal amount of quality real maple syrup or raw honey to the melon. Don't use normal, store-bought honey as it has been processed, refined and heated to kill anything useful in it. Mix and add water. You dilute it with quite a lot of water. Normally half a lemon will make a big glass, just experiment to get the taste right.