It's starting to get hot here in north central MO. The best thing I've found is H20, plain old water. I like it cold, so I pack 6 bottles in a small cooler on ice. Depending on how long I'm fishing, I may drink all of them in a four hr trip. I've had days in really hot weather, that it seemed like I couldn't drink enough water. An ice cold Coke may taste really good, but doesn't do much except to make you more thirsty. An added benefit of packing my water bottles in a small cooler, is that the empty plastic bottles go back in the cooler. I dispose of them when I get home. I think A- Jay posted a chart showing the effects of dehydration. It can happen to anyone, especially in really hot weather. There's lots of different drinks out there now to stay hydrated. And, it's important to remember: if you ever reach a point where you can't pee, you could need medical help. What's your method for staying hydrated when your fishing in the heat?