For me, it;s not a stash, but a working inventory of ATF, engine oil, gear oil and grease. My peak engine oil "stash" (good grief you people) is 300 liters or a 2.5 year supply.
That is not what matters, some feel they know what you need more than you do, and know your storage ability and financial status better than you as well, so therefore feel you are an idiot for having a "stash" of a consumable product purchased at a lower price.
Everyone has something in their lives that others feel is stupid and a waste of money, yet some feel so high and mighty telling other people what their needs are, being ignorant to the facts of others needs and desires.
You want to use the local Walmart (or whatever store) as your stash, fine, pay more for oil than I do.
If you feel that saving $10 on an oil change is not a big deal, then by your reasoning (knowing better for others than they do) I could call you and idiot for not being financially responsible and saving money anywhere and everywhere you can.
But I don't, because how you spend your money is your business.