+1 for Berdar's link above.
Me? This is what I use when working in or near water:
On the knife (blue handle) sheath is a waterproof tinder container. Attached to the knife lanyard is a flint fire starter thingie, and a Lansky Dog Bone for blade touch-ups. All gear is stored in the pocket on the back of the PFD:
Nature's way of culling the herd? Sorry if that comments offends anyone, but if one is dealing with moving water, one should really take a moment to think about the situation. Safety first.
And do you really need to immerse yourself and/or float downstream to cool off? Take of your shirt, dunk it in the water, wring it out a little bit, put it back on, find a shady spot, and let the evaporative action cool you down.