I've gotten to the point where I even start preparing for themes that haven't happened! Last fall, I figured someone would inevitably have a theme about food, and I learned the Robyn Hitchcock song "The Cheese Alarm" so I'd be ready when the day came. Five months later, we still hadn't had that theme, so I just gave up an posted the song on the video board.
A couple months ago, I started learning a tricky instrumental on the grounds that "If we ever have THIS theme, I'm gonna play THIS song!" I would do it for the instrumental theme this week, but I can't quite get through a clean take yet. But by gum, by the time we have THIS theme, if we ever have THIS theme, I'm a-gonna be ready!