Sometimes plain water. Sometimes water with a wedge of lime. Sometimes I'll add a spoonful of sugar to the limey water.

I might throw in an ounce or two of juice. It's good not only for flavor but to keep away (or mask?) the plastic flavor of the bottle.

On our century ride a couple of weeks ago, I drank some Gatorade. I don't think it's beneficial unless you're doing a big haul.

I picked up some of those Caribbean sodas on that century. I don't remember what fruit flavors they were but they were super delicious, because of the occasion.