Well your car only plays CDA, compact disk audios, the ones you buy at stores. You need a MP3 Car CD player. And then you can burn 8 plus hours of music on one CD-R and play it and not hear the same song twice.
if using nero, just make a new data cd and add the mp3 files that you want to it and burn
if using iTunes you must go into "settings" and change to mp3 cd (not audio cd), then add files you want to a list, insert the blank and in the bottom right corner click burn mp3 cd