June, I'm so glad you're enjoying this WOE!
Sounds like you have good plans in place for the party. Bringing things you like will help a lot. You may want to make a 3 bean salad (homemade to avoid the sugar) to share with others--I find that if other people eat what I'm eating (even when the food is totally on plan), it helps me feel less deprived. You look around and other people's plates look somewhat like yours and you don't feel so different.
While you're at the party, notice the things you may have been missing before by focusing on food. There are so many things to do that I never did before because all my attention was on food. For instance, get in the pool with the kids...it's hard to eat when you're splashing in the water!