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.