This is a Vietnam era Zippo cigarette lighter made famous (or infamous depending on your point of view) by photos and television images in the 1960s and 1970s. These images showed American infantrymen burning down bamboo huts of Vietnamese peasants suspected of enemy sympathy or activity.
Besides being a cheap souvenir of your time in Vietnam it became a necessity for tobacco and marijuana smokers. The lighter also came in handy for heating bayonet tips in order to get leeches off your body, for sterilizing the P38 can opener necessary to open C-Rations, and a dozen other uses. All in all a very versatile and handy tool.