Repentance

The best thing to do if you mess up and eat something you shouldn't is to "repent". I call it this because it is so similar to repenting from your sins. Recognise that you've done your body wrong and then don't do it again. Don't just give up and eat whatever garbage happens to be around eat healthy the next day. Recognise that everyone makes mistakes, YOU made a mistake, it won't ruin all of your plans as long as you do better next time.