If you’re a fisherman or boater, you can always clip your pocketknife to one of those floaty foam boater’s key fobs. If you’re way too cool for that (or if you don’t need another bulge in your trouser pocket) you can drop $26 plus S&H for this cork-handled floating knife . . .
A bulky knife with a single tiny blade? I do some canoeing, but this knife gets such a profound “meh” reaction that it doesn’t even quality as an Obscure Object Of Desire. The foam floaty key fobs work way too well to spend money on this.
YMMV, however. If you really want one, you can find them here.