Ah, the garbage bag. This elusive luxury item which throughout history has been reserved only for people who have lots of money.
I listed garbage bags specifically because I've noticed recently that the "good" ones (like, large, or strong) are actually quite pricey and often only are available in large quantities (40 count or something). So the price to buy trash bags might be like $20 or something. Buy 2 at once? $40 on garbage bags while grocery shopping? I mean that's a lot, no? To get the good version of something, twice? Not exactly an item for the poor to double-up on.
And suggest the poor buy the less good trash bags that are cheaper? Well then we have shown that garbage bags can indeed be a luxury item even today.
We buy the big store brand box ($15 - $20 for 200). The box is a bit too big to put under the sink, so we put half in another smaller container under the sink. When we refill that container and the box is empty, then it's time to buy more.
Nothing is forcing you to go buy double everything each time you shop.
If cash is tight but you want to implement this scheme, buy an extra unit of one household item (e.g. laundry detergent) your first trip. Hext time, choose another item (e.g. trash bags).
Eventually you've got a backup unit of every item, and you're now just buying your one item on the same consumption schedule, except now instead of replacing the item you're replacing the backup.