Its not twice always, its just twice once. Its like getting ahead of the usage schedule.

When you start, buy one. You assume its good for 20 days. Buy next one on Day 10. Voila, you have the backup now. Now buy next ones, one at a time on 30th, 50th, 70th day. You are 10 days ahead of usage, you always have at least 10 days of runway ahead of you.

Yes, I do it for Grocery, Ice cream, Watet, Olive, Garbage Bags, Dryer Sheets & anything I use regularly.

The ones in use are required in their place. The spare ones can be stuffed at upper shelves, under the sink, under bed or such.

I have seen second toilet roll in many offices & homes, almost every car has a spare tyre, & many other things.