If your subject is in the shade, compose your shots so that you avoid the sky as much as possible. That way you avoid getting an exposure that's all white sky.
Wipe the camera lens frequently as water droplets may distort the image.
Waterproof housing: Critical... You are not that good!
Helmet mount: Great for catching the action as you see it... and any tumbles.
Suction mount: Position at the front of your vessel to capture the upcoming excitement of face the camera towards you to capture your grin and/or screams
Buoy: Sometimes you want the freedom to capture the action from several angles. Attach a buoy to the base of the camera for a comfy grip... and incase the camera goes on its own adventure down the river...
1. You and your mates are bound to fall in a couple of times, make sure the camera is set up to capture them all
2. Launching and landing
3. Your mate screaming as they head down their first rapid
4. Chances are you will be traveling down a pretty stunning part of the world, try capture a few shots of the scenery too.
5. Underwater shots of your paddle and vessel
6. Chill time on the river bank where you catch your breath after that last series of rapids.