You can burn up to 700 MB of MP3 files as a regular data CD, you will not lose quality, the MP3s will still sound just as good (or poor) as they do when you play them on your computer.
Your friend will be able to listen to the songs either on a computer or a CD/DVD player or indeed a car stereo system that is capable to encode MP3 from data CDs, which is a fairly common feature today.
If your friend's car stereo doesn't support MP3, then there are other ways, such as using a normal MP3 player. It is possible to get the signal to the car stereo in a variety of ways (e.g. with an analog cassete tape adapter or a 12V FM transmitter which can be tuned in with the FM radio).