Throw it in the freezer! I used to waste so much food, it makes me cringe. Now, we are so much better about it.
I save tiny bits of meats and vegetables for future casseroles and soups.
Right before tomatoes go bad, I throw them in the freezer. When it is time for a tomato-based soup or chili, I roast them in the oven (often with onion and carrot) and then put them in the blender to make a soup base. I also add all my saved little little bits of beef from roasts or tacos to the soup.
If it is just a spoonful (like ten peas or corn) I will put them in the "stock bag" in the freezer. I also add to this onion peels, bell pepper tops, stems from broccoli, celery, parsely, etc.
Once I get a chicken carcass from a roasted chicken dinner, I will add the contents of the stock bag and a bay leaf, and make a giant pot of chicken stock.
I have also found that we are more likely to eat leftovers if frozen. The fridge gives you only a day or two, but the freezer gives you a few weeks. That way you aren't sick of eating the same thing.
If you do use the fridge, use a see thru container and/or plastic wrap. If they can't see it, they won't eat it.