What's in your office...
...that no one in any other field would understand your having there?
For quite a while I was the only youth minister in Upper Michigan with a 40-pound bag of quick setting cement in his office. We used it to make stepping stones for a youth group day on ebenezers, or monuments in a place where God did something really cool.
In St. Louis, I have this: it's a microwave potato cooker, but I use it to play "What is it?" a game where each youth group member has to take a random object and instantly make up a use for it, without naming its actual function.
What do you keep in the office that flummoxes people when they see it for the first time?