Depending on the wood, all it may need is a wax finish. Desert ironwood, cocobolo, goncoles alves, kingwood, african blackwood, and several other species is hard enough and has enough natural oils and wax in them that its hard to even put a sealer into the grain. Most collectors I know use Rennaisance Wax on their handles for preservation, both for woods, and some of the ivories, stag, etc. Actually, what works about as well is plain old Johnson's floor wax or a similar paste wax that is heavy on carnuba wax, or gunstock wax. If you use it on wood that does not have a gloss finish it will feel 'tacky' in the hand, and a lot easier to hold onto when wet.
If the wood of the handle is something that needs more protection....has an open grain, it would not hurt to wipe it down several times with a commercial wood sealer, or something like Birchwood Casey's Tru-Oil. Wipe off the excess, then when its dry buff the surface off with a fine scotchbrite or steel wool to remove any of the finish that is on top of the surface, and wax after that. You won't get a shiny finish, but more of a satin finish that will still show the grain.