My worst ones have always been physical contact and crowds, especially noisy crowds. (The exception of this is when I attend baseball games, because when I'm at a game I'm in a whole other world, one where I'm safe from everything.) Because of all of this, I, like many people on the spectrum, can only receive really tight hugs and don't like the feel of certain clothes. I also hate loud people - it rings in my ears.
Enter my paternal
This year, I actually knew why, and it made a huge difference for me. But knowing and understanding your own triggers for your sensory overloads doesn't mean they won't happen, and this is one I can't just avoid, since she's family. At most family holiday dinners, I get headaches and need space because of her and others - when she yells, everyone else starts yelling (hey, we're Italian). I invariably end up removing myself and finding a place where it's quieter just to relax and talk to family members one-on-one as they move about the house, which is a lot easier for me to handle. I still have to eat, though, so I do have to spend some time at the table. That time usually consists of me propping myself up on my hands and eating quickly, namely just because a) I'm hungry and b) too many people can be really overwhelming for me.
When we can't avoid our triggers, what should we do? My best options include bringing something comforting with me to the table, like a pad of paper to draw on, to keep me occupied. It also helps when the cats show up because we've got turkey - Mittens is omnipresent around the holidays because turkey's a favorite of hers. The cats are always something really comforting to me. You may be viewed as a little immature if you bring a comfort item to the table, but feel free to calmly explain what it's for - if it's your family, they should understand, and if they don't, then make sure you have a talk with them about that at some point.
Remember, the holidays are supposed to be fun, so make sure you can enjoy them, too!