I think meals are a significant part of a family's culture, and represent their heritage and history. Celebrating and staying in touch with the members of our extended families is a way to better understand and relate to people around us, and a way to learn about our heritage and ancestry.
Many families don't have "special" meals together at set times or on certain holidays, but statistics show that about 80% of families worldwide, traditionally celebrate "major holidays and events" with some sort of meal together - it sounds like it's the norm. (I am not sure exactly what defines a "major holiday or event" however.)
That said, I think as veg*ns, we are responsible for our selves when it comes to the large gathering and family meal, and bringing things we can eat (whether Grandma approves or not) is always a good idea.
I have two side dishes, a salad and a dessert that are really good (even omnis like them) and are easy to transport. They're my standard addition to any celebratory meal where I'm not the cook in charge...