More people than we care to think about are hungry, lonely or both on Thanksgiving Day. (and every day) Various organizations need volunteers to serve meals, deliver meals, visit with elders and more. Little Brothers Friends of the Elderly is a national organization that delivers meals and visits with elders. They have chapters in many urban areas. In the Bay Area you can sign up for Thanksgiving here.
You might also keep it local and check with a shelter, church or nursing home in your neighborhood. Any small organization could almost certainly use a hand. If you’re busy on Thanksgiving, it’s good to know that most of these organizations serve hungry people every day and welcome regular, committed volunteers.
In San Francisco , The San Francisco Rescue Mission needs help with their block party for Tenderloin Residents. Also in San Francisco, Glide Memorial Church serves meals to 4,500 people every Thanksgiving. It's an incredible, high energy place to volunteeer. They’re looking for help Thanksgiving Day and also donations of food and turkeys.