During my shopping rounds today I stopped by this restaurant for a soft drink. I had it at the bar. When I asked the bartender for the bill he said "it's on me" and didn't charge me for it, even though I've never been there before and hadn't ordered anything else today. I left $2 anyway.
I know, a diet pop from the soda fountain probably costs the restaurant one tenth of one cent or something but it's the thought that counts!
On the other hand, maybe it was just too much bother to do up a bill for such a small item!