With regard to my kids' leftovers, I know it would be better for myself (and not negative for the world) if I just threw it away.  But I lie to myself and tell myself it's wasteful, to justify me eating it.

That was exactly right, though.

There's also some bad faith sunk cost thinking that I engage in. The junk food I've already purchased, I treat as though it's free, because I have no intention of replacing it (that's the bad faith part).