I have disks full of MP3s which, if played in a compatible player, will indeed play for several hours. We had a car player that would do it,(and even had an input jack which would take a minidisk or tape player) but had to junk the car and the new car will NOT play anything but standard CDs.

For my van, which I do not drive much, I have a tape-player adapter that I can plug my portable CD/MP3 player thru, and play any portable device.