Rocketscientist
Marksman
Night sights, and a light, sure. Those things are practical and useful. More mags, absolutely. Factory only like others have said. IMHO, however, don't go messing with the internals of the gun. They are perfectly fine as-is. Training is the key above anything you could possibly buy. I have my first G22 that is still shooting perfect after 15 years and countless thousands of rounds. I wouldn't change a thing about it.