We've talked about them for home and now it's time to make sure you have one in your car that is RATED for use one electrical, and fuel fires.
These type of Fire Extinguishers are more $$ but can be useful to stop a blaze from overtaking your entire car if you get to them fast. If not, then just step away.
I suggest getting one that is rated for your car, but also can be used on a brush fire too. Only get 2 if you can tell the apart in an emergency.