Sounds stupid but some of the old songs from scouts and guide units were quite effective. My scout unit was a sea scout unit and the people who ran it were either ex-navy or worked in boat yards. We sang everything from "hullaballo balay" to "My baby has gone down the plug hole" to "He's my brother sylvest." If you have kids yourself in the scouts, guides etc ask what they sing. They are always rounds, usually folk, music hall or naval.
The songs are simple and can therefore be taught to large crowds of people without hassle.
with regards.
pete.