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I’ll tell you what I do, burning my music files to play on a regular CD player:
Grab the free software Burrrn, drag your mp3 files into the Burrrn window, and it converts and burns the files into a regular music CD for you.
Burn at 16x for best results (this is what Burrrn is set to by default).
Nero will also do this if you select the “Audio CD” template before dragging your files into the Burn window.
However, car CD players are notoriously picky, so make sure you have good blank discs before you start.