Thanksgiving is not the BEST source for holiday movies.
The best movie surrounding the holiday is "Planes, Trains, and Automobiles". Unfortunately it isn't streaming anywhere for free. It will probably be on cable at some point this weekend. But who can wait for that? You can pay to rent it on Amazon or iTunes if you're dying to watch it.
Otherwise...these might be your best options.
DINNERS OF DEATH - SHUDDER
Shudder is a streaming service for horror movies that I'm a big fan of. If you remember Friday and Saturday nights on TNT, there was a show called "Monstervision" and host Joe Bob Briggs broke into the movie with little facts and stories about the scary movie TNT was showing. He has been resurrected over on Shudder. Over the summer, he hosted a 24-hour marathon that broke Shudder's servers. He's back on Thanksgiving for a smaller marathon. He promises to screen his favorite movie of all-time in this block of programming. (Rumored to be one of the first two Texas Chainsaw Massacre movies). He will return for a similar marathon over Christmas.
MYSTERY SCIENCE THEATER 3000 : THE GAUNTLET - NETFLIX
Mystery Science Theater 3000 or MST3K for short is similar to Joe Bob and MonsterVision in that it was a show on cable in the 90s that talked AROUND movies and has now been reborn on a streaming platform. MST3K is a bit different in that they made fun of the movie DURING the movie. It's on Netflix now with a new host and they are doing a 6-movie marathon this Turkey Day. The highlight of which will be "Mac and Me", one of the single worst movies of all-time.
LADY BIRD - AMAZON PRIME
I tout the joys of Lady Bird every chance I get. There's a scene that takes place on Thanksgiving, so it totally counts. (Plus, there's NOT A TON of Thanksgiving movies. Even fewer that are worth a darn) Lady Bird was nominated for five Oscars last year. It is the sweet story of a high school senior who wants to leave home for college. She feels her parents are overbearing, like we all did at that age. If you have a mother, you should watch Lady Bird.
ROCKY - CRACKLE
Crackle is a streaming service from Sony. It's completely free and no one really knows about it. You do have to put up with a few ads during the movie, but it's nothing like watching it on TV with a commercial break every ten minutes. Rocky has a Thanksgiving scene, so again, it counts! Bonus: Creed 2 is in theaters now (Full review: Sunday 11/25 at 8PM on The Josh Odson Show) and you need to watch Rocky IV and Creed to catch up and prepare for Creed 2.
YOU'VE GOT MAIL - HBO NOW/HBO GO
This Tom Hanks/Meg Ryan rom-com has TWO Thanksgiving scenes, so it's not even up for debate about whether or not it counts. A movie that feels like a warm cozy sweater. Two lovable actors, a great love story, and the big 90s nostalgia bomb! It's got EVERYTHING you need for the holiday season.