Hi Jillybean,
Just to answer your question, I always document those days I eat more than I planned to. I think you can learn alot from them, for instance you might of eaten 2 chocolate biscuits mid-afternoon when you weren't supposed to, because you perhaps mistook thirst for hunger. Therefore, you can make a note on that day to perhaps drink a glass of water when a biscuit urge appears and so forth.
I also like to highlight the foods that I shouldn't of eaten, and make a note of how many calories I would of saved that day if I hadn't eaten them. That can sometimes be a shocker, but I reckon that if you have a bad eating day, and your exercising every day or most days, then it won't of made that much difference to your weight. And you can always start afresh tomorrow.
Though, I think Honeybunch's suggestion could actually work - you could designate one day a week where you have a take away and treat yourself to some wine, instead of baked potato and salad, and stick to a healthy breakfast (cereal and fruit), for lunch a salad sandwich and a yoghurt, and then for evening your once a week treat. In this example, it is your take away and wine, or it could be a meal in a restaurant.
I think it could work, but you would have to still keep most of your designated day fairly healthy, I think, for it to work.
Hope this was of some use
Anna