Thanksgiving was originally a holiday observed in the United States of America and Canada on Earth that enabled people to celebrate being thankful for what they had. It was still celebrated as of the 2370s.
During Charles Tucker III's childhood in the 22nd century, his father placed a Thanksgiving turkey on their dining room table, not knowing his son had removed all the screws. The table collapsed, and Trip was subsequently grounded for a month. (ENT: "Observer Effect")
In 2266, the crew of the USS Enterprise were prepared to celebrate Thanksgiving. Captain Kirk was irritated because there was not any turkey on board the ship; the crew was going to have to eat meatloaf instead. Kirk was later informed that, while in the ovens, the meatloaf mysteriously transformed into turkey. This transformation was caused by Charles Evans, a boy with incredible powers. (TOS: "Charlie X")
In 2372, Benjamin Sisko invited the entire senior staff of Deep Space 9 to Thanksgiving dinner. The captain had been growing vegetables for months to serve at the dinner. A year later, Michael Eddington told Sisko that he thought his former commanding officer had added too much tarragon to the stuffing. (DS9: "Blaze of Glory")