My extra pistol mags are stored in the ammo cans for that caliber. For each caliber I typically have a can setup for each: Handloads, Range Factory FMJ, Hollow Point. I put trashy but useable mags in Handloads can because that is what I shoot most often. I put 4 of my best mags for each pistol model in the HP can. All other “nice” mags go in the Factory Range can for that caliber.
Each .50 ammo can will hold close to 1,000 rds. Very little space left in the Handloads can when I have reloaded a batch, and fair amount in the other two for maybe 10-12 mags each.
All of my .22LR mags are in one large MTM sport box. All AK mags are in a large plastic tub. Maybe 60 or so AR mags are loaded and stored in their respective cans (Factory Range, Target HP, SP, Handload Range); I don’t store loose ammo except for a deep reserve can and a test loads can. I think about 15-17 AR mags fit per can (450-500 rds). Another 80 empty mags are stored in a large plastic tub.
Likewise, Garand clips are loaded up in the Range cans, and empty clips fill up their own can (boxed ammo in the Target and SP cans).