It really depends on the gun. If I'm carrying my Bersa 9HC, then a single spare mag in the pocket is good and a second spare at home works. For the 1911s, I have 4 grade A mags (Wilson Combat) and a handful of grade B mags for the range (Kimber, Springfield etc). In general, I like to have 4 spares for each type of gun but don't have any intention of carrying all 4 at once.