"If you cannot tell what it's made from by looking at it, then it's not real food."
I would change this a bit and say the ingredients should just be whole plant animal or fungal foods only, no extracts or processed derivatives or anything synthetic or refined. Nothing you couldn't make yourself using the whole food. So no refined flours, sweeteners, juices, oils, etc.
The point of this is to keep it simple. When I go to the grocery store 90% of what's there doesn't fit my criteria and I don't even consider it. Restaurant food or prepared/packaged food is almost all out since 99% of it is made with ultra processed ingredients usually oils/sugars/flours - I don't look at it as an option. If I'm really stuck there's usually nuts or cheese or fruit for sale anywhere.
So I'll buy vegetables, whole fruits, meat, eggs, dairy, butter or meat fat for cooking with, nuts, seeds, and mushrooms.
For social reasons I'll eat things outside of this on occasion in small amounts but whenever I'm providing my own food which is most of the time, these are the rules.