If you know your creator, you would want to praise Him at all times. This would include even the times when you are travelling. This can be done when you use music to give him praises. Maybe you have some CDs or MP3s that praise him, you can play them in your car and he will be impressed. You need to praise and honor God with your belongings and the car is one of such.
You must not fear looking at the car stereos. They are not worldly things as others imagine. Technology has advanced even on spiritual issues. You can have bible readings that are recorded on CDs and listen to them from your car. You can even have bible based dramas and play them on the car.
These are just a few of the things you can do ensure that you are making the best use of the car. Whatever faith you have, you would agree that you have that car by the grace of your creator. Show appreciation for that. You will be doing that when at least you praise God in that car.
With the best and even affordable car audio systems, you have no reason at all to miss on that. Unless you do not want then you can miss out. If you have the will, you will surely have it.