If you are fortunate enough to work in a sociable, friendly environment, then the chances are you will be invited to (or even expected to) take part in various activities to celebrate Christmas. These can be costly, but I've found a few ways of acting intentionally to make them more frugal. If you are the person who is prepared to organise and coordinate the activities, then you can make sure they fit your budget! Here are a few example;
Christmas cards - instead of all the cost and hassle of giving cards to all your colleagues, organise a charity donation instead. Suggest that people might donate a nominal sum, such as a pound or two, and send out an e-mail greeting to all colleagues with the names of those who donated on it. This can be cheaper and easier than churning out loads of cards, and you know that the money isn't going to be wasted, but will help a god cause. One year we did this in my workplace, and were able to buy lots of dog food, to donate to a local animal rescue centre.
Christmas lunch - instead of going out to a restaurant, organise a bring and share lunch. I used to do this a lot at my previous workplace, and it was a great way of spending time with colleagues without involving a great deal of expense, or even effort.
Gifts - in some workplaces, gift giving is fairly common, and you end up spending lots on token gifts which you know are only going to end up gathering dust somewhere. Instead, a Secret Santa can be a much better option, so that groups of oil leagues only end up buying one gift, instead of half a open. Alternatively, you might collect contributions to raise money for a charity, or one of those buy a goat for a third world family type things. That will probably cost less, and you know it's being used for something worthwhile.