I just put about 13 CDs of music on a mini-USB stick (very short) this morning, and the 'c' plays them nice!
NEW SanDisk 8GB 8 GB Cruzer Fit SD USB Micro USB Flash Pen Drive SDCZ33-008G | eBay
You can use the radio controls to pick out the folder & song you want to play, or you can play them all in random mode.
If you don't like the song that's playing, you can use the steering wheel buttons skip it (and adjust the volume, or jump to radio or CD player).
It's neat to have 15 hours of good tunes without commercials..