I spend almost as much on magazines as I do the original gun. I not only have several for carry (at least three) but also have two sets to rotate and train with. I also have a forth set for Dry Practice.
I do not rotate sets on purpose but it seems to happen about every month as I do extensive training at least monthly (1,000-2,000 rounds).
More important than the quantity of course is the quality. Everyone should carry at least one spare magazine and it is a good idea to have at least one back-up in case one of the two you use malfunctions.
2 is 1,1 is none...
Best Regards.....
"Train to Defend, Train to Survive, Train to Win"