Modern cars usually are fitted with a decent sound system and many allow you to connect your phone or mp3 player to it via Bluetooth. This means long gone are the days of having to carry around a wallet full of CD’s only to find that when you do put one on it is scratched and won’t play. Bluetooth is not only good for your music but also for making and receiving phone calls hands free (although it is not recommended that you make / receive calls even using this method if you can avoid it).
If you have an older vehicle, you could always look at purchasing an after market stereo. These often require additional parts of the dash board, such as stereo surrounds, to allow them to fit in to your particular make and model of vehicle. Although this can be a great way to boost your sound system, you may find that it is actually the speakers that are causing the lack of bass or quality of sound and need to replace them too.