We just had Thanksgiving in the U.S.- a holiday that is notorious as an opportunity to indulge in whatever food/drink you want and (hopefully) not feel bad about it :)
It is definitely important to have values about what you put in your body, but in a strange way it actually seems healthy to allow yourself to "go off the deep end" at times.
By doing the opposite of what is sustainable or ideal, sometimes, you can actually realize more clearly why you maintain discipline the majority of the time.