I spend a good bit of time underway- and can say that I would feel completely naked, powerless, and worthless if I did not have a leatherman on my belt- my current choice being the
Charge. But I usually have a knife as well, and it is usually one of
these. A few other things I never go to sea without-
Pelican flashlight
Petzl Headlamp
I'm pretty hard on my gear, and I can say that all of these are pretty indestructible and can last well in an environment that tends to eat gear- as an example I still have my first Sabrelight that slipped off my belt going through a cargo hatch and fell 55' onto a steel deck and barely had a scratch.