A child taking to the road is a scary event in every parents life. One way to focus that energy and try to be excited for them is to look at what your child needs for their first car, especially in terms of keeping them safe and the vehicle in decent condition.
Seat covers are particularly important in a teenagers car. This shouldn't be a hard one to convince them of with all the different styles out there they are bound to find something they love. The reason you want them to have seat covers is to keep the actual car as clean as you can. Most teens have very messy bedrooms, and now they're going to take those messy habits to their car.
A mix of various emergency supplies can be kept in their trunk. Teens are well known for not making this a priority so it will likely fall on you to make sure these things are in there. These things include a flash light, small shovel, spare tire, bottled water, and a blanket.
On top of this you'll want to have printed directions on how to change a tire unless your child is very mechanical. They were hopefully taught how to change a tire in their drivers education class, but most kids forget once it comes time to actually do it. Having some directions in their glove box might come in very handy.
A GPS unit can be a great idea for a teens vehicle. Once teens get behind the wheel alone they love to go driving around for hours, and often end up lost. These systems also come in handy if they're going somewhere they don't know, or if a road they usually take is closed for construction or bad weather so they can reroute. There are a lot of stylish, simple to use, units available that will talk them through driving to their destination. There are a variety of ways they can be hooked into the car these days, too, so that they're set up in a less distracting way.
While your kid learning to drive can be a frightening experience, focus on what your child needs for their first car, and trust that you've taught them well enough to handle the responsibility.