I like your style, enrious! Though in my game world, a couple of PC races genuinely have the mechanical ability "Eat Anything", so I fear I am back at square one
That said, I have been completely unable to find a good term that encompasses metals, minerals, plants, animals, etc. all at once. Well, except "thing", which is no help since it's already in use. I'm thinking "Species" and "Substance" or "Material" are the way to go right now. Associated tag domains might look something like Animal/Plant/Microbe/Supernatural (the last being for things like angels and demons) and Mineral/Metal/Liquid/Gas/Plastic/Wood/Foodstuff/Fabric/Arcane (et cetera - what would you use?), respectively. I realise there's a bit of overlap between the two categories, especially for things like woods and foods, but you could differentiate based on existing distinctions: "Maple", "Maple Wood" and "Maple Syrup", for example, or "Cow", "Leather" and "Beef".
You could also use creature origins as apply to your setting, like Natural/Elemental/Shadow etc. in D&D, since those would regularly apply to non-sentient plants and substances as well as monsters.