Pay a stranger's way

This morning I walking on campus and I found a $20 bill on the floor, I looked around to see if anyone had dropped it.. nobody. So I figured I could use a coffee.
As soon as I got to the window, I remembered this kindness act plan, and paid for the order of the person behind me and mine with that money.
Then later, I bought a water bottle at the gas station for the older gentleman selling strawberries on the curb with the change I had left. He then thanked me because he had been out in the sun all day and was parched. He had the biggest smile on his face, and that was the biggest reward of it all.