Never leave your dog in the car alone on a warm day. It can be hard to go to shop with your dog but if you have to leave them in the car just make sure you put down the window a bit so they can get some air. Also, make sure your no longer than 10 minutes because you don't want to come back to seats ripped or something worse.
Take breaks during long car rides to allow your dog to stretch their legs, go to the bathroom, and get some fresh air. This also gives you time to stretch your own legs!
Make sure your dog is comfortable with the car before trying to load them in. Bring them on short drives around the town, gradually increasing the distances so that your dog gets used to the car and they relax, then you can take them for longer journeys.
Keep a supply of water and a bowl in the car for your dog to stay hydrated. Even pack two bottles one for yourself and another for your dog to fill their bowl. It may lead to more pit stops for toilet breaks but atleast we are both hydrated.
Keep a supply of treats or a favorite toy on hand to encourage your dog to get into the car. You can also use a command that you have trained your dog to associate with getting into the car, as long as your dog is happy to get into the car and go on some adventures with you. And when you arrive if its for a hike or a swim you have toys for your dog to play with.
If your putting your dog in the front or back seats , make sure you have a harness to keep them from roaming around and keeping them safe in case of accidents. If you would put a seatbelt on yourself why not ensure your dog has one too. Also its less distracting as your driving your car because you know exactly where they are.