Depends on the gun!
I got about 30 Extra 1911 45acp mags, so I may have as many as 40-45 for one 1911??
seriously a lot of my mags are changeable like the EAA mags and the CZ mags.
I can likely round up 5-6-7 mags for most each gun I have but I shoot for at least 3 for each weapon, pretty sure I have that at least.
even the Sig 238 has 4 mags for it.