I agree that it's a time of year where you're a bit thrown. It's not like a normal holiday from SW, for example a week away lasts just that week, but at Christmas things tend to start cropping up before the actual day itself, the odd Christmas drink, sweets at work, etc.
I think it's a good idea to have something resembling a plan.So, if you know you're going to be eating big dinners on three days, you could make a decision to cut back on the other days. Or to have a couple of Success Express days. I'm off work for nearly 2 weeks, and have a few dinners planned out with friends. I intend to enjoy every bit of it, and if I want extra desserts or whatever I'll have them. But, that's part of my "plan"... to allow myself those extra treats and syns, I'll balance it out with low syn breakfasts and lunches, stocking up on superfree, cutting back on carbs. 2 weeks off work means I've no excuse not to do some walking.
If I get to 20th December without an idea of what I need to do to keep on track, I'll lose the run of myself. So now is the time for me to make frozen low syn meals etc that I can depend on at short notice.