I think the more you plan the easier it is. What I mean is just saying you are having a day off means you can have anything (including all that carby, sugary stuff that sets off the cravings) and makes it more difficult to stop. If you say, maybe, you are having dinner that evening and can get as much detail in your head as possible and it is not so easy to add things on. Does that make sense? It's just a bit of headology and has worked for me a couple of times. Plan, plan, plan then in your head it is part of the diet.