I reckon if there is something you have *really* been fancying and your mind keeps returning to then you are better off deciding that you are going to do it and enjoy it. That way you are making a conscious and controlled decision about it rather than feeling like eating and cravings have got the better of you. It seems that sometimes a day eating things you don't usually have, or quantities of things you don't usually have, can boost your metabolism anyway. Maybe some fairly meticulous planning of meals after your day off plan would help? That way your cupboards and fridge are full of things you like and want to eat and you have some favourites to look forward to?
When I first started doing SW I would plan a day off about once a month but after a while I discovered I didn't really want to eat any differently than the rest of the time so it would end up just a case of having a couple of glasses of wine or some unmeasured cheese on a baked potato.
I reckon the good thing about WW is that it doesn't cut out anything we like, therefore having one meal or one day off plan is a bit safer as you aren't having to return to total deprivation afterwards.