Ed rented a car recently and it came with Apple CarPlay. Is that secure? Leo says it is because Apple makes it really difficult to break encryption. You just want to be sure to remove your device after you're done with the car rental. Select "Forget Device." Or don't use the car's internal telematic systems. Just the CarPlay.
There's also a setting in Apple CarPlay that says "do not copy my contacts" to the car. Make sure you enable that so your contacts won't get transferred to the car's hands-free system.