Yes. DF had 2 cartons of coke in the trolley, put the other items up to be scanned, forgot to tell the cashier that he had the coke so she could put it in the machine, walked out with 2 free cartons of coke.
He realised when he got home, and called them. They said not to worry about going back to pay for it, too much hassle.
I once gave DD2 a box of coffee sachets to hold, she was being a sook so I was trying to distract her. I forgot to get it scanned. I called when I got home and they said it wasn't worth going back in for a $3 item.