A couple of years ago I posted about a photo rig for kayaks. I like the setup but it is mainly for pretty committed bird & wildlife photography (serious tripod & head, big lens, etc.) As I was getting ready for a little paddling trip a couple of days ago with my 7-year old son, I devised a simple little way to have a camera at hand in the boat without the major rigging job. This method works well for moderate setups like 100-400mm or 80-400mm zooms on DSLRs, for a smaller kit like a mirrorless DSLR rig, or for a super-zoom camera.
The thing about kayaking is that lots of splashes come on board from the alternating paddle strokes. The little cups on the paddle shaft help to keep much of the water outboard, but even on a sunny day there's going to be water droplets sprinkling down into the boat. Putting your camera in a dry box (such as a pelican case) or in a dry bag will keep it snug but deployment will be slow if a bird suddenly appears. As a compromise, I put a boat cushion down on the keel in front of me to rest my camera rig on (this pads the camera and keeps it up out of any water pooling up on the bottom of the boat.) Then I drape a dry bag over my camera to shed any droplets coming aboard. If a photo opp presents itself I can just pull off the dry bag & grab my camera. Also, if things get dicey (like heavy rain, waves splashing into the boat, etc.) my dry bag is immediately available to slip my camera into for a more secure storage situation.
As I said before, mixing camera gear with watercraft amplifies the risk factor significantly. When deploying a camera in a kayak or other small boat you are always one mistake or accident away from unrepairable disaster so get real familiar with your boat and check your rig on dry land before attempting! Oh, and have fun!!