Water is a must in the desert, but I often carry something caffeinated as well. Such as: Red Bull, Coffee or black tea (for morning games), or a Dr. Pepper. Every now and then I will go for an original flavored Gator Aide.
I have a gallon jug of water with me during the summer. Nov. to March I sometimes play with no drink with me, after the round I get a pop. I like G2's or gatorade and have a pouch in my bag for one if I choose to get one.