Guy in front of me paid for a bag of ice at the dollar store and had like $3 and some change left. He told the cashier to use it to go on my order because he said someone had done it to him earlier. I only had a box of crackers for my chilli, and some cookies. Guy behind me had a gallon of milk. The first guy had already walked out, so I told the cashier to just use it on his milk. I know it's just $3, but it was still a nice gesture.
Many moons ago we were at a Mexican restaurant in Georgetown in DC sitting on the patio. People at a table near us left and the server brought over a pitcher of margs and said they bought it for us.
We bought another table a pitcher, they then bought another table a pitcher. Always wondered how long that kept getting passed on that night.