The best way to become a vigilante superhero is to arm yourself with an arsenal of nonlethal weapons. Batman is one of the most realistic superheroes, in that he has no superpowers. Rather, he is highly motivated, informed, and has his utility belt full of gadgets.
There are many nonlethal loads calibrated for existing firearms and shotguns like rubber bullets, pepper loads, and powdered teargas. Shotguns can also fire tranquilizer darts. There are also specialized grenade launchers such as the m79 or mm-1 for firing gas grenades of any kind, adding knockout gas to the list. These grenade launchers with their larger bores can also fire 'bean bag' loads, heavy shot-filled bags which can knock a man down but not kill them.
There are also many hand grenades with nonlethal applications, such as the flash bang, which only makes a loud bang and bright flash which temporarily stuns everyone in the vicinity. These are often used to diffuse hostage situations and bank robberies, when strike teams or vigilantes must discriminate between the guilty and the innocent.
Other nonlethals include solid objects fired at nonlethal speeds like ring airfoil rounds. These are paper cylinders, looking a lot like an air filter for your car but much smaller, about 3" in diameter, which fly aerodynamically so they go pretty far and can be aimed with fair accuracy, but are nonlethal as they crush on contact and feel like a hard punch. These use the propellant from a blank .223 (5.56mm NATO) cartridge from an m16 or similar rifle, and require an adapter affixed to the muzzle.
There is also a sticky foam in use which shoots highly pressurized foam, much like a fire extinguisher, and hardens into a resin. This could be dangerous if aimed at someone's face but extremely effective on the legs and arms.
Electrical devices like Tasers and stun guns use electricity to overload the body's central nervous system but will not stop the heart. Other electronic devices use sound. Pain field generators emit a frequency that causes head pain, dizziness, and confusion until the subject backs away from the origin of the sound. There is also an ultra low frequency that causes subjects to lose bowel control and crap themselves, but I'm not aware of any devices designed expressly for that purpose. The drawback with these sound devices is that they affect everyone in the vicinity, and therefore require that operators be in some kind of sound proof shelter like a riot vehicle or a safe distance from the device, because the vibrations affect your whole body. Plugging your ears doesn't help.
Finally, there are melee weapons like nunchaku, bo staff, bullwhip, baseball bat, crowbar, batarang, escrima sticks, police nightstick, etc. Some of these require a little skill to use effectively so your mileage may vary.