Nothing, they don't celebrate it.
Probably laze around the house as the exam weeks are over (for those who are students), or continue to work like nothing happen. Moreover, it is shadowed by their own new year festivals.
I can't pull out of my mind someone who will actually celebrate it. Maybe some characters who are from earth would cook special meal and bake cake or cookies for the sake of festivities. (None of them are actual practicing Christian or Catholic)
New year is when the festivities at