Nope for me, 1 Cougar, 15 rounds. I'm good with that. My pockets are already full of other stuff.
I feel if I were to have a magazine failure then I'm probably just SOL. Here's my reasoning, you get a jam or a FTF. 1st step is clear the jam and chamber a new round. If it jams again, you now have to eject the magazine, clear the round, insert a new magazine, and chamber a new round. That's a lot of time and it assumes it's the magazine that is bad and that the one being dragged around in your pocket is better. I think I'd take my chances on clearing the 2nd FTF and just try loading a 3rd round. In a true SD situation you'd be lucky to accomplish that. For me I'd re-seat the slide and use the DA mode to strike the same round again.
I guess if you've had problems with magazines or ammo and you've had to fiddle with the lips to get things to feed right, then I'd be more inclined to carry a spare, but then again, I'd be even more inclined to carry a different gun.