Since today is New Year's Eve, and since the New Year was one of the times given to wassailing, I am posting a song that falls, at least part way into that tradition. It is actually bits of three songs, arranged as one by Peter, Paul and Mary, and which they call A Soalin'.
There are actually three traditions combined here, as well as three songs - there is an old custom, of which I was completely unaware, called souling, in which people would go from door to door on All Souls Day (November 2nd), to sing and pray for the dead, and in return, they would be giving a soul cake The modern custom of trick-or-treating is thought to come from this older tradition. It is very similar to the wassailing traditions, which could take place any time between harvest, to just before early planting, which would be around February, although, it was strongly associated with the New Year. And with God Rest Ye Merry Gentleman tagged on at the end, we've come to the familiar caroling tradition, which we practice now. There is a bit more information to be found here.