I don't do much nowadays, but when I do, it usually includes patter, jokes, and/or slagging off the announcer or a singer who is coming after me. After me, because I pick on people who can hit back.

Oh, and I sing as well.

Probably the neatest one I ever did was when a boom mike wasn't clamped tightly. As it sagged down, I sang "Alas our mike has listed, at 45 degrees. It is a handsome chrome thing, but I'm singing on my knees!" (White Cockade, of course.)
Good cheers for that one.