Try not to leave your cat alone in the car, but if this is unavoidable leave the car out of direct sunlight and with all windows open.
Never leave your cat unattended in the car for any length of time - remember a car on a hot day quickly becomes an oven.
Your cat may be anxious at first but eventually most cats fall asleep.
It is possible that your cat may suffer motion sickness and so it is not a good idea to feed it within about an hour of the start of the journey.
Once your cat is used to the container, feed it inside there and shut it in for short periods before travelling.
There should be a dish of water and dried food may sometimes be useful on a lengthy journey.
If your cat has a favourite toy, put that in its carrying box.