Social Security Card
Tons of people seem puzzled as to why I would need a physical Social Security card. The answer is that I need it as proof of Social Security Number in order to (belatedly) convert my New York driver's license into a DC one.
Incidentally, service at the Social Security Administration office at 2100 M Street was very prompt. I'd sort of been expecting an interminable wait during which I could make a serious dent in The Conscience of a Liberal but my number got called almost as soon as I was finished filling out the brief form. The employees working at the office were polite and helpful. Bureaucracy works!