When the double album Johnny Cash at San Quentin (1969) was released, a good bit of the show had to be edited out for space. The DVD special edition released in 2000, featuring almost the entire show, includes performances by supporting players Carl Perkins and June Carter Cash.
One little nugget Cash wrote just for this show, the song San Quentin, was the highlight of the evening for the inmates, but sadly left off the initial release. Here it is below. Even if you are not a country music fan, check it out -- it's an unparalleled musical commentary on prisons.