alt Hacker NewsUSB front slot with USB memory sticks? One stick per playlist/album. Different form factors so you can locate the right one without taking your eyes off the road. Possible to embed into larger enclosures if you find them to small.
(Personally, I do prefer the modern Bluetooth+mobile+app+voice control).
I rocked this setup for a while, and it wasn't terrible. My only mistake was to buy 20 identical USB drives, but a sharpie helped to some extent.