Spare Headphone Adapter
The iPhone XS comes with one spare headphone adapter, but if you lose it, you'll be annoyed that you didn't pick up a spare when you were at an Apple Store.
If you use a line-in option to listen to music in your car, you may want to buy an extra one of these and connect it directly to a cable with a zip tie or tape so that it isn't lost.
You can also look into a Belkin Lightning to 3.5mm jack if you want to connect your iPhone to the car without worrying about an adapter.
For anyone that doesn't switch to Bluetooth headphones or the AirPods, this is an essential iPhone XS accessory. You can pick one up from Apple for $9 from Apple.