Like everybody, I have a range from 1 (1921 Luger) to 32 (Colt LE6920)
I generally stock:
5 for CCW pistols, so I don't have to download mags for range sessions. I usually run stages with 1 in the gun, and 2 on the belt. For CCW I carry a spare, so 5 seems to work out about right.
10+ for a match pistol, or anything I'll use in a class. I'd rather listen to the instructors, or shoot the bull than load mags.
I've only got 5 magazine fed rifles, 3 are suitable for HD ext. so they run from 10-32 mags each.
Sometimes like in the case of my HK45T it takes a while to get there at $62 per and shipping, but eventually I do. As we used to say, mags are a "Class IX" item and disposable, you should expect them to wear out/break (not anytime soon at %^^&%$$ $62 a pop though).
Chuck