I'm going to one at my parents tonight.

Gotta be careful. You are supposed to drink 4 cups of wine (!) but you don't have to finish them and then there's all the matzo and a festive meal as well.
My plan is to have less than 10 oz or so of wine, total, a couple matzos (they're only 100 cal each and my mom gets whole wheat), a reasonable serving of a side dish and entree, and a reasonable portion of dessert. I hope to leave without feeling all bloated and gross like I usually do.