Leatherman Micra.
Yeah yeah yeah it doesn't open one handed, but man do the spring loaded scissors come in handy.
You also have a couple little screwdrivers to tighten the handle on your reel, and the blade is the perfect size for getting rats nests out of the line. But best of all, since we know that fishing flat out requires craft beer, it has a great cap lifter.
It also happens to fit into that smallest pocket on the front of your fishing vest... you know the one... that doesn't fit anything more than a bic lighter and a couple of split shot weights. Yep, it drops right in.
Very affordable, durable, reliable, versatile, and comes with an unbelievable warranty.