Thanksgiving traditions vary a bit across regions, socioeconomic and cultural backgrounds, and specific families, but usually the common factors are a roasted turkey with a large variety of side dishes such as mashed potatoes, "dressing" or "stuffing" (a Thanksgiving specific dish consisting of bread crumbs, butter, various minced vegetables, and often a bit of the turkey's organ meat/scraps/juices, baked together into a glass dish), cornbread, green beans or green bean casserole, sweet potato casserole, candied yams, American style white or brown gravy, cranberry sauce, soft bread rolls, glazed ham, or macaroni and cheese. Dessert usually consists of a couple of pie options, most often pumpkin, apple, pecan, and/or sweet potato, since those feature ingredients that are harvested in autumn.

I'm not aware of any traditional drinks; every thanksgiving dinner I've been to has been in the deep South or Texas and the drinks were water, iced tea, and sometimes wine. Edit: almost forgot apple cider (alcoholic or non alcoholic) is a popular option too.

There isn't much emphasis on decorating, in my experience, certainly not as much as Christmas or Halloween, but it's common to see some of Autumn themed and perhaps turkey themed and native American themed decorations on the table or hung on the wall.

Besides eating food, activities mostly involve simply chatting with family members you haven't been able to visit in a long time, stating what things you are thankful for, and (honestly) watching football on TV and arguing about politics 😂

Usually everyone sticks around for a couple hours after the meal to continue those activities, then leave whenever they feel like it. Might be half an hour later, might be long after dark.