WASHINGTON - What's in the wallet of Timothy Geithner, whose hands as U.S. Treasury secretary are on some of the fattest government purse strings in the world.

Not much, it appears, beyond a few bank cards, some euros and a worthless Zimbabwean bill.

Geithner, testifying to a congressional panel on Thursday about efforts to tackle the financial crisis, was shown a $50 billion bank note from Zimbabwe that has nearly no value due to hyperinflation in that African country.

Representative John Culberson asked Geithner if he had ever seen such a bill himself, prompting the Treasury secretary to reach into his pocket and produce a Zimbabwean note.

I often have some foreign currency in my wallet, Geithner told Reuters during a break. Want to see?

Many of the slots in the thin, weathered leather wallet were empty. There were three cards with Visa and MasterCard logos -- all inserted upside down so the issuers could not be seen -- and a yellowed identification card of some sort.

From inside, Geithner pulled a small pile of receipts and papers, including a New York City transit card, pointing out there were some euros tucked in there too.

Anything else? Not a single U.S. dollar was in sight.

(Reporting by Jim Bourg; Writing by John O'Callaghan; Editing by Dan Grebler)