Use a rock or a stick or whatever if that's all you have to stay alive.
There are situations that may call for more than one mag but they're rare and, for the most part, foreseeable. I recall catering a bike rally at a Harley dealership, there were clubs there that might take exception to patches others were wearing at that time. In that case it was four spare mags but everything was fine and a good time was had by all.
While shot placement is key, I don't feel you'd usually be fighting someone determined enough to shrug off a leaking hole of any caliber.
I guess this is sort of pertinent, but during the big biker shootout in Waco, I think at least one of the deceased was rendered that way by a lowly .380.... IIRC, of course.
Sort of lends credence to the "use what you have" idea....