I basically accept that for gatherings like that, I'll be very careful, but I can't avoid getting a bit of sugar. It's a bit like what the book says about a kid's birthday party. If they end up eating sugar one day, it's not the end of the earth, you just get back on the horse the next day.
Having said that, I ate dessert in restaurants two nights in a row last week and put 1 kg back on. It fell off just as quick, but, it's a reminder of how much too many 'just this once' moments can derail you.
I'm travelling to the US for three weeks with work, and I will be in restaurants a lot, so it was good to be reminded of that.