For long paddling or hiking trips, I will often bring along my Camelbak water pack. I used to pooh-pooh these things, believing they were just another piece of extraneous gear, but now I am a big fan. They carry so much water in a simple, convenient way, and they really help you stay hydrated. Basically, a good Camelbak is like carrying around two big Nalgene bottles, but having your hands free and/or not having them darn things dangling from your hip.
But onto another point regarding Camelbaks. You can now buy electrolyte tablets for the water inside them, effectively turning your water into Gatorade. I used to doubt the usefulness of electrolytes, but a few years ago I was on a long bike trip, drank some after a grueling ride on a hot day, and found my energy surprisingly restored, my body wonderfully refreshed. The Camelbak Elixir tablets come in lemon-lime flavor that is said to be perfectly tasty, and just one of them dropped into your Camelbak water is enough to keep your salts up for several hours.