Lock n' Load
Custom
For me, one spare mag in case the one in the gun fails. Your needs may differ. Carry what makes you feel safe, ready, and able to stop the threat.
Why are you so adamant that no one should carry 2 extra mags ? Most people, including professional instructors, will tell you to carry as many as you can comfortably carry and/or conceal.
If you’re worried about getting in a firefight, carry as much as you can comfortably. That being said, a firefight is generally not the kind of circumstance you’ll find yourself in, exceptions being law enforcement or turf wars. I’ll bet most of you reading this aren’t the turf war type though. I may carry more than one magazine someday, however if I needed to use more than 14 rounds on 1 or 2 attackers at close range I would be mortified. If someone is still coming after 3 maybe 4 rounds of hollow point, maybe I should be more worried about my aim than if 40 rounds is going to be enough for someone with a gun who wants to take my car.
This is by no means advice, but a point of view that was shared to me by an experienced shooter and longtime concealed carrier after I consulted him about the same question, “How much ammo should I carry?”