I remember one of my first family events after I was diagnosed. It was for my cousin's graduation party. Although my aunt really tried, the meal consisted of cous cous, a gravied chicken dish, chicken parmesan, a noodle salad, a regular salad, bread etc. You can see where I'm going with this. My aunt had known I couldn't have the chicken parm, but she didn't know the gravy had flour in it, or that the cous cous also contained gluten. She felt horrible that I had barely anything to eat.
The major thing I learned from this occasion is that if you're going to be going to another person's house for an event and you don't want to be left standing with an empty plate, you need to step up and educate the host. Even if it makes you feel a little uncomfortable. By doing this you can spare both yourself and the host from an even more uncomfortable situation. Offer to bring a dish yourself, that way you'll know that at least one dish will be prepared in a way you can eat. I usually bring a dessert, because most hosts are more comfortable making adjustments where needed while cooking, but are not comfortable with the more tedious baking adjustments. On my recipe page you'll see two desserts I recently brought for Thanksgiving. So before suffering through the marathon of holiday parties with your stomach growling this December, try being your own advocate and find yourself some good tupper-ware for transporting. Good luck!