Aim to consume somewhere in the neighborhood of one 750 ml bottle of water and/or sports drink every 1 to 1.5 hours. If it's hot and/or if you know you sweat a lot, go for a bit more.
As for sports drinks, I use HEED. I discovered that Gatorade gives me mouth sores, and I've never really liked the flavor. I recently tried GUs sport drink and it seemed all right too. It also has maltodextrin, like HEED, rather than the simple sugars Gatorade has.
As for electrolyte replacements, you can go natural, and eat things like salted almonds, potato chips, dried apricots, bananas, etc., or you can get a pill (I have a bottle of "Essential Electrolytes" I use on hot days), or you can get flavored electrolyte "singles" in the powdered drink section of your grocery store (check the section where you find your Crystal Light and Nestea singles).