SLPT: When grocery shopping, if you see something you were going to buy in a person's cart, feel free to take it. It’s not stealing because the other person doesn’t own it until they pay for the item.
True story, I was grocery shopping and accidentally walked off with another shopper's full cart. I Pushed theirs around for several aisles before I realized it. I went back and got my cart, and wonder to this day if the other shopper ever got their cart back.