Catherine, I don't have an "invisible third" but I can sympathize. DH has a weird issue I think of as chronic leftover syndrome. He always has to leave a little bit undone, whether it's a woodworking project or cleaning the house OR FOOD. I'll make a meal for two, assuming there will be a left over lunch, and come out to the kitchen to see that two tablespoons of taco meat (but no tortillas) are still sitting in the pan, along with a teaspoon of chopped onion but no cheese. Or the bag of potato chips I thought had one serving left really has about half a cup of crumbs (but it's been neatly sealed up and put back in the snack basket.) Or there is a tablespoon of popping corn left. MINDFULNESS, people, MINDFULNESS!

Eta - Catherine, if I were you I think I'd set aside the next-day portion right at the time the food is cooked. For myself, I'm trying to be the food manager, even though I resent it a little it's better than living a life of weird little meals made up of the least interesting food on the table.