Negroni, i don't think this applies totally to your situation, but i've C&Ped some Getting Back on the Wagon tips that i put on another thread below.
About friday - it's 4-5 days away. you have basically two options if I've understood your post correctly (apologies if not):
(a) think to yourself 'well i'm going to cheat on friday so i might as well go the whole hog and cheat (to a greater or lesser extent) until then'
(b) think to yourself 'i'm going to be going mindfully off-plan on friday and enjoy every mouthful. until then i'm going to stay on-plan, then get back on the wagon after my meal out'
you know what will likely happen with thought process (a)? you will keep having 'accidental mini cheats' (as an aside, in what way are they accidental?), gain weight, feel crappy on friday and not make the most of your planned cheat. the cheats between now and then won't be worth it, you'll only be eating them because you've 'allowed' yourself to do so. you'll have perpetuated the high/low blood sugar cycle, as well as the guilt cycle, and you won't enjoy your proper, mindful, taste-every-mouthful lunch out
with thought process (b), you will arrive at your lunch feeling sleeker and trimmer, and more ready to fully enjoy your off-plan meal
i know this is easier said than done, and i don't always get it right myself, especially when you've got a whole load of parties etc, and sometimes you have to accept that you may not lose very much for a period, or try to maintain or not put on more than a few lb in that time
you need to make the decision about which off-plan foods are worth it (the once-in-a-blue-moon absolutely fabulous not-to-be-missed ones that should be savoured) and which ones aren't (stuff that's readily available, cheap, highly processed, a poor imitation, actually not that satisfying etc).
after you've had your mindful wagon-topple, that's when it's important to be prepared to get back on it, and recognise the siren call of the carbs for what it is. if you don't, that's when you risk getting back into the carb cycle.
BACK ON THE WAGON TIPS
- have you got all the crap out of the house? (as much as you can - i know it can be tricky with family members (and with leftovers), but maybe you could ask them to forgo the carby stuff for a few days while you get back on track?)
- plan your ABSOLUTE FAVOURITE low carb meals for the next few days, breakfast, lunch and supper - you need meals you can look forward to and which make you feel satisfied and indulged, not mediocre ones which get rid of the hunger but don't stop you feeling deprived when the siren call of the carbs gets going
- make sure you have low carb snacks available if you need them (you shouldn't physically need them, but as i'm sure you know, they can help you get through the carb cravings)
- drink plenty of water (i'm sure you know the drill). helps you feel full apart from all the other benefits
- don't try to do too much in terms of exercise while you're combating the carb cravings. if you want to exercise, do, but don't push yourself too hard (i did a 40-min exercise dvd followed by a 5k run the other day and nearly keeled over at the smell of dp making toast)
- change your routine a bit if you can. habits (particularly the bastardy carby ones) are quickly formed, so change stuff about a bit
hopefully some of this helps!