I must advise against tsadjatko's advice on this subject. Many snakes are not able to escape the maze of a car's insides fast enough when in direct sunlight, nor are they wise enough to realize that any dropping temperatures means they must find a warm blanket and a nice fireplace. Many snakes will die in a car because they simply cannot find a way out. And then you have a huge smell on your hands... You can only expect so much from an animal.
I have heard two success stories of owners with lost snakes in cars who recovered their lost pets by placing a small cardboard box (big enough to house the snake, but small enough so that it would be a cozy fit) on the floor of the car right before you go to bed. The box would have a hole cut into the side large enough for the snake to enter, and a warm, thawed mouse would be placed either nearby or sometimes inside the box. This setup is intended to cater to a snake's night-time activities and their superior sense of smell.
The idea is that during the darkness and quietness of the night, the snake may be coaxed into exploring its surrounding, and may become enticed by the smell of food. After consumption, snakes seek a small, dark space (like a box) to curl up in and hide until digestion is finished. Again, I have known this to work twice in the past.