take smaller quantities with you and leave it in your purse...
I'm not sure there's a really good way to tel your boss to keep their grubby paws off your snacks.
At my current office, I've had people eat my lunch out of the fridge... Even if my name is on the bag.. some people have no manners - you really just have to catch them in the act and embarass them - not exactly a career move to embarass your boss
