I have had someone at Starbucks buy me coffee a few times. I have always just bought the next person's drink.
On Valentine's day this year, I had time to kill before an appointment, so I went to lunch by myself. A gentleman walked up and gave me a rose.
This one didn't happen to me but a friend. She is a nurse and after a particularly hard day, she left work and it was cold and wet. She went through the drive thru at Panera to get a cup of her favorite soup. The gentleman in line before her bought her the soup. It was a bright spot in an otherwise crappy day.