You could spend a lot of money for a marine flashlight only to misplace it or lend it out and never see it again. I have.
GreatLite sells a water- and weather-resistant marine lamp ($10) that's perfect for stowing on the boat or in the truck or cabin. Or losing and not caring too much. The 12-inch-long plastic body floats and has a rubber-loop lanyard. The four "C" batteries make it a little on the heavy side, and it's not indestructible, so you wouldn't issue it to divers or Navy SEALS. It does, however, come with a limited lifetime warranty in the event it stays in your possession.