Anakin Skywalker sneaks into the party to be with Padme, and when he gets caught he says he has "jedi business" there.
Obi-Wan Kenobi pretends to not notice Ahsoka and Anakin breaking the rules and finds a nice corner to read in.
Captain Rex spends most of the night watching Ahsoka, making sure she doesn't drink too much, (she does).
The Ghost crew celebrates with a mix of Mandalorian, Lothal, Lasat, Ryloth traditions and end the night with fireworks by Sabine (Hera describes the colors to Kanan).
Finn spends New Years Eve at space Time Square because he saw it on the news all the time when he was in the First Order. He ends up being disappointed and decides in the future to spend it with his love ones.
Din spends New Years trying to give Grogu the best night, at the same time trying to trick him its already midnight so they can all get some sleep.