One of Kondo’s theories is that people who live in untidy environments (i.e., all of us who haven’t been her clients) buy more stuff partly because they don’t realize how much stuff they already have.
She is negative on the idea of stockpiling in Costco-style quantities, pointing out that you’re not running a retail store so it doesn’t matter if you run out.
Kondo never suggests a time period as a way of setting household stock levels. A Costco pallet of paper towels, for example, isn’t a crazy purchase because it may be used up within a month (a friend likes to use an image of an entire roll of paper towels used in a single kitchen clean-up by an au pair to illustrate what happens when people are insulated from pricing, as in health care consumption, for example). On the other hand, in the Amazon Prime age can it make sense to buy a pack of 8 toothbrushes? Or a 16-count Gillette Fusion razor cartridge pack (Dorco might be better!)?
In an American suburban home with basement and garage, why wouldn’t it be reasonable to keep two months of non-perishable consumables somewhere in the house?
More: Read The Life-Changing Magic of Tidying Up, by Marie Kondo.