Every year, our office get a big tin of wonderful toffee. I haven't eaten a bite of it for the last two years.

Also, planning ahead about what I'm going to eat and not leaving anything to chance.

Eat mostly healthy stuff. Healthy stuff tastes good and makes you feel good!
Have one cookie, then stop. None of this, "oh the hell with it".
Keep working out.
Drink lots of water. And green tea.
Weigh self once a week as always.
Treat yourself to the more expensive healthy foods that you normally would think too expensive. Like exotic fruit, for example.
Remember that parties only happen now and then, and for just one meal that day. The rest of the time eat healthy.
During the party, eat mostly the healthiest choices, then maybe a bit of the junk. Then stop.
Never more than one drink per day. For me that would be wine.
And keep working out!

avoid carbs, and have healthy alternatives on hand when I go out/about to parties and what not. I've been on a weight training/low carb plan for almost a year and have dropped 85lbs. Never thought counting carbs was a legit way to lose weight, but I'm happy I was proven wrong.