Real answers should be slightly stupid anyway. Action movies run on cartoon logic.

Like, yes, Mythbusters proved a water heater is a pressure vessel that can flatten a house. But actually trying to weaponize that is fucking ridiculous. Especially if it's got fins welded on like WW2 ordinance, and it's delivered by trebuchet.

Mythbusters also demonstrated grain-silo explosions with just about anything powdered. They launched a bunch of powdered non-dairy coffee creamer into the air and it became an unreasonably dangerous fireball with a mushroom cloud. And that material, powdered creamer, is presumably long-lasting, widely distributed, and in limited demand. But you'd have better luck throwing a bucket of it at someone's head than trying to aerosolize and then ignite some... vanilla-scented starch.