Nowadays Thanksgiving seems to serve three purposes. The first is the traditional celebration: to gather with family and friends, eat and drink, and give thanks for the good events of the past year. (It's handy, this, because even if you've had a really shitty year you can probably still find something to be grateful for: "at least I have my health" etc.)
We were invited, with the in-laws, to a party at the house next door. Good fun, and excellent food: Gary, the host, takes cooking very seriously. Thanksgiving food is similar to Christmas food: turkey and stuffing (which Americans call "stuffing" if it's cooked inside the bird; "dressing" if it's cooked separately). Potatoes, although tradition here is mashed not roast. Roasted sweet potatoes (often but wrongly called yams). And green bean casserole, a 1950s invention which became a tradition: green beans baked in cream of mushroom soup and topped with crispy onions.
The second purpose of Thanksgiving is as a bookend for Christmas preparations. While stores here have their Christmas goods out as early as Halloween, after Thanksgiving the Christmas season really gets going. In particular, the day after Thanksgiving seems to be the earliest acceptable date to put up Christmas decorations inside or (another American tradition) outside your home. A couple of hard-core fanatics in the neighbourhood had full nativity scenes in place by the afternoon of the 26th.
And the third is to provide some heavy-duty shopping action: all the big stores here have huge sales starting the day after Thanksgiving and running through into the weekend. And they start early: 6am is common, and some go to 5:30am or earlier. What kind of nutball gets up at 4am, sleepy and hungover from the night before, to go shopping? Not me, but millions do.