My coworkers and I often bring similar foods to work, which means that after a few days pass we aren't sure whose food is whose.
Usually, just to be safe, we ask each other things like, "Is this my yogurt or yours?"
"Did you bring Pop Tarts this week?"
"Are those my moldy leftovers?"
I don't remember exactly when I brought it, but I think it's safe to say that the can of Ensure I found in the fridge today didn't belong to any of my coworkers.