I watched Survival Lilly on YouTube, her latest video shows her utilizing a small whiskey flask for carrying cooking oil. The flask is metal, seals completely, & is easily carried in a pocket or pack. I duplicated the idea in my GHB. I'll also be adding 1 to my BOB.

What other liquids would be used camping in small amounts that a whiskey flask would accommodate ??

Everclear for alcohol stove fuel, antiseptic, and crystal light cocktails.

I can see how a cooking oil explosion would be a giant mess. But a whiskey flask? That's a lot of weight for sealed storage. To my mind, it's easier to use poly bottles inside some sort of crush resistant container.

Besides, as a traditionalist, I believe that whiskey flasks should be preserved strictly for their primary duties, and not abandoned to the dark realm of domestic chores.

First aid trainers agree with you on that, at least sort of . Do not put non beverages in beverage containers and do not put liquor into containers for non alcoholic beverages (and maybe vice versa) to avoid unpleasant and maybe dangerous mixups.
Poly bottles are a better idea as you have a chance to see whats in it.

I have my 8 oz SS hip flask cut off at the top rim. It serves as a sturdy EDC container, protecting my solar charging powerbank in the front pocket of my sport coat. It can be easily converted into a boiling/cooking cup (by prying out the concave wall to increase the volume and using a wire in predrilled side holes to hang it over the fire). When stuffed (with the powerbank, disposable rain poncho, AC/USB charger, USB cable - it is heavy enough to work as an impact weapon.