Here is a keychain multitool for gun enthusiasts. The 3Coil Puna 6-in-1 Multitool has a blade, wrench, bottle cap opener and screwdriver bits. When put together, it looks like a rifle. The blade measures 0.875″ long, weighing 0.9oz.
The 3Coil Puna multitool is available for under $50. More info is available here.