The majority are worth pennies -- except for ones like the 1943S copper pennies. Coin collector Bob Campbell says the coin is one in a million.
"A coin just like this just recently sold a few months ago for $1 million," Campbell said.
Campbell purchased his precious penny years ago, and it cost him $20,000.
"So it's been a pretty good investment so far," he said.
There are only 20 or so known 1943 copper pennies that were minted from San Francisco, Denver, or Philadelphia, and they're mostly in the hands of collectors.
But what makes it valuable? The US was not supposed to make copper ones in 1943 because...
"They needed to take the copper out of the pennies to make shell casings for the war effort," Campbell said.
So the '43 pennies were made from steel. But according to Campbell, a few copper ones were mistakenly minted and put into circulation. Collectors have been looking for this prized penny for decades.
"It's a fantasy coin. It's a coin that people spend hundreds of hours looking for," coin dealer Jeff Berkoff said.
So what are the odds? Can you really find something of value in your pocket?
"About one a decade gets found right now. And when they come to market, they're worth quite a bit of money," Campbell said.
And it's not just the '43 pennies that are valuable. The 1955 double-die penny is worth over $25,000. There's also the 1937-D three-legged buffalo nickel. It can go for over $1,000, based on its condition.
Even the youngest of collectors have plans if they find the million dollar penny.
"It's just cool, and I probably wouldn't even trade it," coin collector William Wilks said.
If you do come across a 1943 penny, grab a magnet. If it doesn't stick, chances are it's real.
Word of caution: There are counterfeits out there so be careful. You can contact the Greater Houston Coin Club, and they can put you in touch with professionals to help prove its authenticity.