I came up with a lighter gun that's inspired by the tiny one from Ace Attorney: Dual Destinies' Final Case.
It can function as a regular lighter, a laser pointer/gun, or a covert gun. The lighter function can be used to start fires or melt things like locks. The laser can do the same but in long distances, but can also be used in junction with the Gun as a laser sight. The gun utilizes tiny ammunition and while it can't pierce armor, it's useful for getting past security and missions where you need to be carrying as little as possible.
The cartridges are also easy to carry in hidden pouches or pockets so you can change them when no one is looking.