While I can't suggest not looking at uni work at all over the Christmas holidays, it's important to be realistic. It's more realistic to expect the opportunity to get started on revision than to complete all of it. If I manage to look at a couple of textbook sections and reinforce my knowledge of one or two topics, I consider that a success.
There's also the matter of work for things other than uni. I don't plan to write articles over the holiday season or work on many other uni-related endeavours. I do enough of that during the school year and since it's not strictly required of me, it can wait.
For working on Christmas preparations, that's a different matter entirely. I typically don't put work into them unless other people are willing to help me, due to the amount of time and energy necessary. I also don't put effort into things I know I'm not expected to do. If I think people will appreciate the final product, though, I typically go ahead and make the crafts or cook the soup.
For many of us, spending time with family can be work as well. I'm fortunate to have a good relationship with my family, but that is not always the case. Some people have to care for family members as well, which can take a lot of energy. I recommend taking some 'alone time' to recharge, regardless of your situation. Socialising with other people can be exhausting at the best of times - remember to keep your own well-being in mind.
Ultimately, the question of how much work you should be doing over Christmas depends on your course, your family situation and how you celebrate. While everyone will approach this challenge differently, remember to make time to relax before returning to uni!