Presumably one just tucks in, enjoys it and then starts afresh the next day. Right???
The 'how will I feel if I eat this, immediately and in the day 24hrs thereafter' time works pretty well in most circumstances.
How will you feel if you pick this event to indulge? Glad to have joined in? Or glad to have had one mouthful and crumbled the rest? Glad not to have been tempted. Think it through and decide what to do.
If you go for it, the thing is to draw a line immediately. Drink lots of water and climb back in the waggon immediately.
Avoid the f*ck it moment that drives you to eat everything in sight for hours, days or even, like me earlier, years ....
Consider the association you have between food and pleasure. It is entirely possible to celebrate and have fun, with a glass of water and no sweet stuff. To feel the urge to indulge, to have a plausible excuse ready and simply sit with the feeling, allow it to exist and still not indulge.
If you give in, the temptation will return, even stronger than before.
If you don't give in to it, it gets weaker.
You get to choose...