I think most seemed to have missed the point. Scafool seems to have come closest.

The point is to keep survival kits, and all gear attached to you, compact and streamlined.

While keeping a knife easily at hand sounds like a sound solution in this case a knife may have been exactly the wrong solution. Slashing desperately and blindly at a grab line while being buffeted by whitewater sounds like a fine way to hole the raft. Tangled in the grab rope of a raft is bad. Tangled in the rope of a raft that is no longer stable and under control because a major flotation chamber is holed is far worse.

Now I don't object to having a knife of some sort handy, options are good, but the knife has to be used with great care and only where it makes sense. Also the sheath and knife have to be mounted and positioned in such a way that it does not create a risk of being tangled. Some thought might be given to the sort and size of blade you carry. Knives designed for use around life rafts often have blunt points and it would seem to be common sense that the blade should be relatively short. Most knives purpose built for survival use around rafts seem to have blades only about 3" long. A shorter knife would also seem to be less likely to get snagged or cause unintended damage.

Survival gear in general should stay out of the way until needed and impose the minimum burden possible on the person carrying it. Small and light with a few well selected and highly adaptable pieces is better than a larger kit with more specialized gear. Particularly if the kit gets in your way. The most important, and comprehensive piece of kit is what you carry in you head.