Have the ingredients for a puzzle, but can't settle on one.

So I’ve been kind of fiddling with this idea for a puzzle for a while. Basically, it would involve taking a “do not eat other peoples’ food” from one fridge, and moving it to another…but what purpose would it serve? Here’s a couple of ideas:

An NPC who has an important item would walk by the fridge occasionally and check it for food; putting the sign in the fridge, along with some rotten food (or food laced with sedatives, or poison, or something along those lines), would cause the NPC to sneakily grab the food, eat it, and then fall unconscious/die, allowing the player to take the item.
PROBLEM: Well, for one, it requires a few strange leaps of logic, and overall it kind of feels like a ripoff of the coffee/pills puzzle from Little Blue Men.

Or, the player needs to store some food in the fridge for later use (say, due to a limited inventory or something), but needs to prevent the NPC from stealing the player’s food once it’s in there, by placing the sign in there as well.
PROBLEM: There’s no reason for the player not to put the food anywhere else in the game. It’s not like the NPC is some kind of ultra-determined food-thief who will try to snatch up the player’s food as soon as it leaves his/her inventory.

So, what do you guys think? Is this simply a lost cause, and I should look for other puzzle ideas? Or is this a salvageable idea?

If your concern is simply to come up with a plausible reason why the player should have to put the food in the refrigerator (thereby raising the further problem of how to keep it out of the hands of the victuals-thief), doesn’t making the food highly perishable give you enough of a reason? (I.e., you could keep it in you desk, or your pocket, but then the ice cream would melt or the fresh fish would spoil. Thus, only the refrigerator keeps the food in edible condition.

Robert Rothman