I would love a locking feature on refrigerators! In addition to keeping visitors from eating all your food, it would be great for when you have a Sim with the Glutton trait! Sims with that trait eat constantly whether they're hungry or not.
Also, I'd finally be able to keep a birthday cake in there instead of putting it in the household inventory so others don't have a chance to eat it before the birthday.
Plus, it would solve the frustration of impatient household members grabbing food out of the fridge to eat instead of waiting for the meal another Sim is currently cooking for them.
Lastly, the family cook could even prepare appropriate meals for breakfast/lunch/dinner ahead of time and then call to meal. Might even help with those who like to take screenshots of families eating a meal together at the table at the same time. Especially if you have Parenthood. Just keep place settings on a dining table, call to meal and voila! A nice family dinner shot for stories or whatever. :)