If you can’t think of something nice to say to the person sitting next to you, trade memories of the dearest, departed loved ones you share a connection with who are no longer sitting at the table at all.
Pick up an instrument and play music together, or sing some old hymns of Thanksgiving (“We Gather Together” was always my favorite).
Take a walk, breathe fresh air, go out on the deck and make fire-pit s’mores (or use the gas grill).
Show the young ones at your gathering how to make rubber-band stars, advanced paper airplanes, origami hearts, or crochet snowflakes.
Get silly. Play Charades or Spoons or Balderdash. Laugh at yourself and laugh with your relatives.