My best advice is to eat right before you leave to go to the shower(s), or if you are helping with the setup, eat right before it starts. If you aren't hungry, it should be easier to resist eating. This worked for me on my first week when we had our quarterly birthday celebration at work. I had to actually cut and serve the cake, which I ordered, and I was really looking forward to it. It was hard, but I made it.
And remember that if you do have a piece, make it a small one (try half the size you would normally get) and that if you are otherwise sticking to your goals, one meal/day where you go a little over isn't going to hurt you....just continue with the program the very next day.
Hope this helps!