Bag? Ziploc!
A lot of kayaking is done during the day; the *middle* of the day. The light isn't often all that spectacular that having big lenses will be all that wonderful. Maybe for some long reach (back to the shore), but I'd probably leave most of my equipment in ziploc bags and inside my backpack until something specific came up worth shooting.
In the meantime, I have a water-proof, shock-proof, freeze-proof, zombie-proof, bullet-proof (well, maybe exaggerating those last couple) camera that I keep with me *out* of the bag. This is a case of the "best camera" being the one that you have with you. Mine is a Panasonic TS series, but Olympus makes several good choices as well. That, or GoPro. This is exactly what these cameras are designed for.
The shot that I'd want to reach for the bigger gear would have to be really special. Even then, kayaks can flip really fast when your attention is on something other than safe boating. This I know... 
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