If you use lacquer to finish the heads of your fishing flies (economy flies omit this step, and they fall apart), then you'll be glad to have something to clear the eyelet. I barbarically often use another hook.
Handiest thing to have in your pocket is a finger nail clipper for clipping fishing line. First read that in "Taps' Tips" in Field and Stream magazine in the 70's. You can cut close to the eyelet very easily---WAYYY better than with a pocket knife, where somehow you'd have to get a hold of the short end I suppose. Same goes for cutting close to a blood knot. It's hard to imagine doing that with a pocket knife. A lit match will help in a pinch. A pocket knife would be handy for marking wood, say to preserve the length of your catch before you released it.
Bill