This just happened a week ago:
So I'm cycling along a 4-lane street in a nearby town, and just after passing through a traffic light, I need to weave through some auto-accident debris in the bike lane...wait a minute...one piece of debris was not like the others.
Stopped, went back and picked up a leather case about the size of a book. One compartment was open, revealing a cracked iPad mini. I opened the other compartment to find a checkbook and credit cards, and a thick white sealed envelope. I stuck the case in the trunk bag on my rear rack and continued on my ride.
About an hour later I reached the convenience store where I usually stop for a coffee break. I pulled out my phone and googled the name and city from the checkbook. I called the number that came up and got a secretary who said the guy was out for the rest of the day, but would call him and give him my number.
A minute later he called. He asked the condition of the case. I told him the iPad was cracked but functioning. He said he had just bought a new one anyway, so that was not a big deal, but asked about the envelope. He said he "needed that". We made arrangements to meet at a shopping center along my route home.
We met at the shopping center, and I gave him the case. He examined the iPad, then checked the other contents. Then he commented:
"I really appreciate your honesty, even though you had no idea what you had."
With that, he broke the seal on the envelope, pulled out a 3/8" thick stack of crisp new hundred dollar bills, and gave one to me.
I'll admit it was a lot easier to be honest, thinking I was just returning a broken iPad, checkbook, and credit cards.