This sounds just like It's A Wonderful Life, but it's a true story out of Billings, Montana. 

This story is just mind blowing.

On Black Friday, Carrie McNeese of Billings, Montana was out shopping for her four children, their spouses and her eleven grandchildren. She was carrying an envelope with $500 cash and a list of people to buy for. After spending $200 at JC Penney, she accidentally dropped the envelope. When she discovered the envelope missing, she figured that cash was gone for good, but she was wrong. A security guard named Reggie Anderson found the envelope, but he didn't just go the extra mile to track Carrie down.

First, Reggie dug through the store security footage and spotted Carrie dropping the envelope. He saw that the list was written on a piece of paper that had Stewart Title Company written on top, so he took a screen shot and sent the picture to Stewart Title Company and asked if anyone there recognized the woman. They did and told him it was Carrie and they gave Reggie her phone number.

Reggie contacted Carrie and returned the envelope with the remaining $300 and her shopping list.