Just be aware that a fire extinguisher will not put out a full-blown fire or even a relatively small fire if it has a gasoline supply. I came upon a car accident a few years ago within a minute or so of the crash. There were several other people trying to get the female passenger out (the driver was deceased). Someone voiced concern about moving her for fear that she had spinal injuries and one of the rescuers said something like, "I'm an EMT, forget her back, we have to get her out NOW." I saw they had enough help there so I focused on putting out the grass fire around the vehicle and then started trying to fight the fire on the underside of the truck. A friend of mine was waving people down on the interstate and bringing me extinguishers as fast as he could. I would spray the fire (the easiest access to the fire, and the closest point to the victim, seemed to be between the bed and cab of the pickup). I started out spraying bursts, but within seconds of stopping, the flames leapt back up. I then sprayed several full extinguishers and again, within seconds, the fire blew back up. At this point, they had the lady out of the vehicle and I was out of extinguishers, so I backed off. A minute later the fire department showed up and gave the truck a burst of foam (which was 10x what I had been able to put on the fire), but again, within a second the fire popped back up. At that point the fire fighter sprayed until the foam completely enveloped the truck stem to stern, which finally put the fire out.
So, an extinguisher is a good tool, but just know that unless you catch a car fire early, it may have limited effectiveness.