A couple years ago, I was riding in Minneapolis with a buddy and he spotted a $20. He bought coffee and pastries that day!
Last month I was on the Almanzo 100 and enjoyed the huge number of water bottles littering the road - but the best was cash ($1s and a $5) was on the road, since the Almanzo is a "race" nobody around me was willing to stop and pick it up. We all pointed it out just in case Scrooge McDuck was in the pack and we could get an advantage while he's picking it up. No takers.