Usually in a shirt pocket or coat or vest pocket on the right breast.
I dont carry an extra mag in case I run out of ammo. In the real world any self defense shooting you get in will be about 3 rounds at ten feet.
I carry an extra mag because in the real world, the majority of auto pistol malfs are magazine related.
According to the FBI statistics from the past 30 years, you can get into two shoot outs a week with a k-frame .38 before you have to reload fellas. Spray and pray looks cool in John Woo movies, but its horse crap.