There are a couple of infamously interminable songs I recall from my days in the back of the bus (usually a bus bearing our troop of Boy Scouts to or from a weekend of camping and improvised mayhem...)

"99 Bottles of Beer on the Wall", of course, headed the list, but it was closely followed by "The Ants Go Marching One by One". One of the great things about such singalongs was that it mattered not a whit whether or not one could carry a tune in order to participate at the top of one's lungs. Another was the ease with which even the rank novice (and many of our little heathen tribe were rank indeed, especially at the end of a weekend camping excursion!) could catch on to the lyrics. Of course, the best thing of all was watching the bus driver's head begin to spin like Linda Blair in a centrifuge after about Beer number 54 had been taken down from the wall and passed around...

As far as songs from the back of the bus that I'd like to sing again, that will take some loooooooooooong thought...