I carry a spare mag most of the time.
I do this for 2 reasons:
1. mag related failure
2. If the situation dictates it, I like having a mag I can just unload to keep someones head down and hopefully buy me some time to get away/to cover/etc... without leaving me with an empty gun.
All the cool kids do it...I do not. But I could probably be convinced to..
It might take more than that