Every car fire I've seen in person was well past the "run away" stage and could not have been knocked down with any fire extinguisher that doesn't come with its own diesel engine. With the small size of my car and all the other stuff I carry, it hasn't been a priority for me to find a reasonable way to carry one in my car.

If I ever go back to a pickup from the four-door sedans I've been driving, I may change my mind.