Hi there - Welcome to Spark and congratulations on taking the first steps toward a healthier lifestyle.
I can tell you how I would handle the situation, and then you can decide if it makes sense for you. Everyone is different, and one person's solution doesn't work for everyone.
I would think about the following things - I'm not suggesting that you do everything here. It's just some ideas to think about.
1) Focus on the celebration first, not the food. I'm not saying ignore the food or deprive yourself of the food. Just shift your mindset to celebrating the overall experience and really savour/indulge in the non-food related elements: the conversations, the festive atmosphere, the clothes, etc. Whatever pleases you.
2) Be selective. Taste, not gulp. For example, if I was at a buffet with foods brought by family or friends who I really cared about, I would try to taste a bit of a number of dishes that have sentimental value for me and the people who made the dishes. But I would use a small plate, I would take small portions, and I'd eat a mouthful or two. And I'd talk a lot and walk around a lot. If I were at a restaurant, I'd "spend my calories" on something special that I wouldn't have at home. I'd share my plate with others - either actually splitting servings or offering up a taste or bite (or six) of my wonderful meal. And I would avoid the ordinary - I'd avoid wasting calories on things like soda, sugary iced tea, etc.
3) Load your plate up with healthy stuff, and take small servings of calorie-rich foods. Make sure at least half your plate is vegetables (or fresh fruit at dessert).
4) Avoid arriving at an event starving. Yes, it can be a good idea to eat a little less the day before, day of and day after your event. Skip dessert the night before and night after. Serve yourself slightly smaller portions of meals. But don't starve yourself, because then you'll probably dive into food when you get to your special event.
5) Go for a walk. A walk isn't going to burn off the calories you ate. But fresh air and movement can make you feel good physically, and that can reduce your temptations to overeat.
6) If there's alcohol, choose options that are lower calorie. Wine and beer, as opposed to cocktails, are pretty good. Alternate water with alcoholic drinks to reduce the calories consumed.
7) Aim to be mindful, not perfect. You've just started Spark and it takes a while to get into the groove. At this stage, being aware of (and recording what you eat), rather than being super-restrictive, is a big step forward. If you can experiment with a few adjustments in your behavior, even better. But don't try to be perfect.