2. Carry enough gun.
Not going to start a caliber war thing, but a sidearm for self-defense must deliver enough force to make a difference.
I don't think handgun caliber makes a difference. More appropriate would be "Carry a long gun" A .223 is much more effective than a .45, even though the .45 is a bigger caliber. If I was in a gunfight, I would rather have a rifle than a handgun any day of the week.