Like PB4 said, avoid straight gatorade. Gatorade has a lot of sugar in it and that sugar can actually make the diarrhea worse. My primary care physician said to mix gatorade with water in a 50%/50% mix. Pedialyte is better since it doesn't have the sugar. Soda can be bad also. I have a big problem with regular soda, if I drink it, it always triggers diarrhea. Diet soda is a bit better, but not much.
Water is your best bet, but make sure you are getting some electrolytes as your body cannot run on water alone. I know that trying to keep the water "in" is tough. When it gets hot here, and I'm working outside a lot, I can get into trouble really quick. Trying to keep up with sweating while not triggering diarrhea is a difficult task.
When I travel, I carry a number of small packages of "oral re hydration salts".
http://www.google.com/products?q=oral+rehydration+salts&ie=UTF-8&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&sa=X&oi=product_result_group&resnum=1&ct=title It's basically the good stuff in gatorade without the sugar. You can just mix the powder with water and drink it. Not as convenient as pre-bottled stuff, but in a jam it works.
"I'm just along for the ride."