Without this urawaza, if I were to look in my refrigerator and see this:
all I would know is I have 1 to 12 eggs.
Now I save an old egg carton cut down to hold 4 eggs:
When a carton of
eggs gets down to less than 5 eggs, I move them into the 4-egg carton,
filling from the front.
Then a glance in the refrigerator tells me I have:
5 to 12 eggs
2 to 4 eggs
Usually it's the act of moving the 4 or less eggs to the 4-egg carton that triggers me to put "eggs" on my shopping list. But the carton is a good visual indicator as well.
What made me think up this urawaza in the first place has more to do with compact storage. Since my refrigerator shelf is 19" deep, I can keep a full carton of eggs behind the 4-egg carton. I used to move any extra eggs to a bowl, but the 4-egg carton better protects the eggs, is just the right physical size, and is always ready to go (when empty I keep it on the shelf it behind the full-size carton).