People who leave laptops or wallets at the airport security checkpoint almost always rush back to get it. But do they return for the pennies left in the bottom of the plastic bin after they've retrieved all the items they emptied from their pockets?
That may explain how the Transportation Security Administration ended up with a hefty cash "tip" of $765,759.15 last year, and $674,841.06 the year before. The 2015 figure includes more than $9,000 in foreign currency and more than $30,000 in small change collected at Dallas/Fort Worth International Airport alone.
Passengers left behind more than $43,700 at New York's John F. Kennedy International Airport, almost $51,000 at Miami International Airport. A hefty $55,086.39 was hauled in by the TSA at Los Angeles International Airport. Last year's collective TSA haul has nearly doubled since 2008, when the agency reported more than $383,000 in unclaimed change.
"TSA makes every effort to reunite passengers with items left at the checkpoint, however there are instances where loose change or other items are left behind and unclaimed," a TSA spokesperson explained to CNBC.
According to the agency, all unclaimed funds left behind at security checkpoints get counted, turned in to TSA's financial office and deposited into a special account. Then, by permission of Congress, the funds get spent by the agency on security operations it deems fit.
In a report to Congress, TSA Administrator Peter Neffenger said that this year, the agency plans to use the unclaimed money collected in year 2015 to support its effort to expand the TSA PreCheck program. That gives passengers expedited passage through security checkpoints, in exchange for some personal data and a fee.
At airports in Canada, unclaimed funds left behind at the checkpoints seem to be dealt with a bit differently.
At Vancouver International Airport (YVR), any currency left at security checkpoints is collected and logged into lost and found for 60 days. If unclaimed, it is donated to local charities through YVR's community giving program, said spokesman Christopher Richards.
Like several other airports in Canada, including Toronto Pearson International Airport and Montreal-Pierre Elliott Trudeau International Airport, Vancouver International also has "coin balls" or "giving globes" in various locations inside the airport. Those repositories are where passengers with spare currency can donate to good causes.
In Montreal, funds collected at the airport giving balls go to Keroul, an organization that makes transportation accessible to people with reduced mobility. And at Toronto Pearson, funds go to the airport's Propeller Project, which last quarter helped provide transit passes for Syrian newcomers in the community.
Spare change collection boxes set up at both Denver International Airport and Phoenix Sky Harbor International Airport, as well as others, also help travelers lighten their pockets for local nonprofits—instead of the TSA coffers.
In 2015, Denver International's coin collection program raised more than $87,000 for a program that provides resources for people who are homeless. Last year passengers donated close to $12,000 at Phoenix Sky Harbor to support the USO center there.
Through UNICEF's Change for Good program, at least a dozen airlines around the world also turn spare change from travelers into good deeds. The list includes American Airlines, whose flight attendants have collected $11.5 million in foreign and domestic currency from passengers on international flights over the past 21 years.
—By Harriet Baskas, special to CNBC.com. Baskas is the author of seven books, including "Hidden Treasures: What Museums Can't or Won't Show You," and the Stuck at the Airport blog. Follow her on Twitter at @hbaskas. Follow Road Warrior at @CNBCtravel.