When I was in college I worked at CVS, on move in day a guy came to buy batteries and was a couple dollars short. after trying to count out his change I told him not to worry about it and just take the batteries. I forgot about the whole thing almost instantly after it happened because it wasnt a big deal. a few days later the guy comes back in, waits in line to buy something and asks if I remembered him. He then told me that I really helped him out that day and he proceeded to leave a $20 bill on the counter and walked out. I will never forget that, the fact that he remembered me doing something so small and then went out of his way to more than re-pay it.