Whats the nicest thing a stranger did for your?

I think the nicest thing a stranger done for me was when i was checking out in a store i was short a dollar and some lady gave it to me..do not know who she was to this day..I feel the nicest thing i did for a stranger was once when i was at a resturant in my town there was this guy who was traveling and he was back packing..he came in to ask for some water, he had no money..so i bought him a hamberburger and fries with a drink..