It can be daunting to have to spend Christmas on your own.

That's one reason why the suicide rate is so high over Christmas, when it seems that everyone is enjoying a family holiday together.
The reality is that it's not all happy families. People put all their energy into having a wonderful time together and it's a time when lots of quarrels and disagreements occur, so that's one thing to think about.

If you are going to be spending the day at home the first thing to remember is that it's only one day out of life. If you are going to be separated from a special loved one, move the day of celebration to a time when they can be with you, even if it's turkey and crackers in June.
Then set about spoiling yourself for the day, but without making a huge fuss about it being Christmas. If you like champagne and a lie-in, make yourself some champagne cocktails and watch tv (but not those dreadful forced jollity Christmas things). If you like movies, make sure you have the latest ready to watch or a really riveting book if you like reading.

Don't go out to lunch. It's really sad watching all those couples and families sharing togetherness, when you are alone.

Either spend time cooking yourself something delicious, or, if you don't want to bother, snack on any kind of treats you like. It's your day.
Make sure you phone a friend, lover or family member during the day. If you are a computer fanatic, spend time browsing sites you don't usually bother with. Go on a virtual journey to somewhere outlandish for example.
There probably will still be a sense of things not being quite right, but it is possible to pass a pleasant day on your own. (Tomorrow the shops will be open and you can take off to the sales)!
I hope you have a lovely day!