Or, like the old joke says, "How do you become a millionaire? Go to Vietnam and exchange $56." For a couple hundred dollar investment, you can get a shoebox size pile of small denomination bills*. Enough to make a TSO think they found the Big Catch™, as most screeners probably could not find Vietnam on a map let alone know a dollar will buy you 17,860 dong. Don't tell them until after they count it.

*Not sure if it is authorized to take VND out of the country these days. It is amusing that places whose currency is worthless/non-convertable outside their border (like the old USSR ruble) have such strict prohibitions against exporting it. Is the cost of printing replacement bills going to bankrupt the country? Heck even China lets you take a few thousand RMB cash out of the country now without declaring it. ^