Black coffee - the stronger the better! Have bought some decaf for my filter to try and start cutting down the caffeine a bit. Other than that I drink cola, soda water and lime, apple juice, mango juice, blueberry juice, elderflower presse, ginger beer, ginger ale and green tea.
The main thing I've noticed the couple of times I've been at events is it's hard to drink the quantity of liquid along with others who are drinking alcohol. I never noticed before really but after 2 large soda water and limes I'm kinna full!