Quite honestly the chocolate milk has all sorts of good stuff usually. Small bit of minerals, fluids, protein, some sugars. Try for a brand that is lower in sugar content and you're good to go.
If I'm going to be doing a longer training session I'll often make myself a small glass of chocolate milk and have a half a banana as a "supplement" before I start. I'll have another small glass (4 oz) afterwards along with the other half of the banana. Did wonders for aches and pains, not to mention helping prevent cramping and simply fatigue. It has helped me when water wasn't sufficient (I sweat a lot too and I live in an area that tends to get hot).