we have a notorious bag and tag'r in our building. Always loads up plates of the food leftovers after meetings and claims it. I want to steal that crap everyday. Really pisses me off when she leaves it in the fridge and forgets about it. 
My former secretary was just like this. Literally hovered around any meeting so she could load up a dinner plate with Jackstack the second it adjourned. She would take 2-3 plates.
In our cafeteria we had vending machines that are free. So soda, gatorade, vitamin water there for the taking. The day she gave 2 weeks, we told her no, just go ahead and leave now, she packed up her belongings and one of our HR ladies caught her trying to load a banker's box with free pop on the way out the door.