Christmas parties are suit and tie affairs. (Not fancy dress, that would be costumes.) I just don't see any public Universities in the U.S. throw so many parties where all the guys show up in a suit and tie. I only had two Christmas parties, one for the student village I live in and the other for my research department. I had my suit but when I looked through my shirts I realized they were all old since I have not dressed up for years. I decided to get a shirt with the french cuffs and cuff links because you can get away with that kind of thing here.
Both of the parties had Christmas Crackers (The big tootsie roll looking things made from wrapping paper). I've always seen them but have never pulled one apart. At the village party they just went handing them out. Once you had one, you found a friend, each grabbed an end and pulled until it popped. Whoever gets the big end, gets the prize inside. There was a joke, small plastic comb, or other small toy, and a folded foil crown. So the rest of the party is everyone dancing around with crowns on their head. At my research party it was a little more formal (apparently there are some low end royalty funding our research so they were at the table with heads of the different groups.) Everyone was sitting at large round tables with a cracker on each plate. To pull on these crackers everyone at the table crossed their arms over their chest and held a cracker with the next person. Everyone pulls their arms toward them. The prizes inside these ones where silver pens or calculators.