I don't care what gun I'm carrying I carry 2 mags. Faulty mags are the most common cause of malfunctions on an auto and having more ammo is never a bad thing.
You could always check the crime reports for your area and see what is common for where you live. I've never heard of a law-abiding citizen getting in an extended gun fight requiring multiple reloads but at the same time it's absolutely no extra trouble or effort on my part to carry a double mag pouch on my belt. YMMV
I don't collect guns, I accumulate them.