How Old Are You?

Originally Posted by BC-Axeman

This is the back of something that if you saw the front it would be obvious.

Originally Posted by Route 66

This is the only one that stumped me.

Man, I must be old.

If you saw the front the tabs would say things like "Whole Milk, 2 qts.", "Cottage Cheese, 1 qt.", "Skim Milk", etc.
You would put it in an empty bottle for the Milkman to tell him you wanted something extra with your usual delivery.