Coughton Conspiracy for Nov 5th (one of my own)
But I usually respond to people in the audience
"Blow ye winds in the morning" for US visitors
Farewell to Nova Scotia, South Australia, Tamaranui (NZ), etc and "Somebody's Moggy" or one of my own in the same mould about rabbits for the kiddies. Halloween, Remeberence Day, Good Friday, and many more but I do have a few alternatives for most occasions.
I find it helps to have a reason for singing other than self-satisfaction.