Housekeeping travails

When you buy extra milk, the carton in use will go on and on, much like the fish in the parable. But if you were planning to make an almost-empty packet last one more morning, the milk will mysteriously disappear.
You will be able to compose a grocery list only in the shower, or some such inappropriate place, where you cannot get to a pencil and paper. Of course, once you pick up a pencil and paper, you will never be able to remember the list.
You will carefully craft a grocery list and then leave it at home when you set out for the market.