I already have a t-shirt from one of the national parks (a long-ago gift from the furloughed Cousin Halbarad). I could put that on, and then festoon a skirt with the Meals on Wheels logo, dairy products for WIC, books for the Library of Congress, an image of the Statue of Liberty, things like that, all with red slashes through them. Then I can wear a sign on my chest that says something like "Due to the temporary shutdown of the federal government, this costume is closed until further notice."
Cheap, timely, workable. What's not to love?