First Contact Day was a holiday celebrated to honor the flight of the Phoenix and first contact with the Vulcans on 5 April 2063.
On Earth, children get the day off from school, a fact Captain Janeway remembered was really the only way they used to celebrate it.
Naomi Wildman and Neelix planned the 2378 observation of the event on Voyager. The festivities included Zefram Cochrane's favorite food, cheese pierogies, and Rock & Roll music on Tom Paris's jukebox. He also had Tuvok recite the first words ever spoken to a Human by a Vulcan, "Live Long and Prosper", and give the Vulcan salute. He didn't see the point of it, but everyone applauded anyway. (VOY: "Homestead")