Since Jan. 19, 1998, I’ve found $971.05.

I know this because, for 20 years now, I’ve been keeping track of every penny, nickel, dime and quarter that I’ve found discarded on the ground. As well as every half-dollar (one), every Eisenhower dollar (one) and every penny with a small engraving of JFK across from Lincoln’s profile (one). I’ve found a lot of loose change through the years.

This...