if you have to work on christmas, well, it sucks, but try to make the best of it, get into the spirit and have fun with the customers.
In between taking Christmas Day pics, I was just in a 7-11 looking at DVDs for sale and the dealer remarked I probably wouldn't find anything decent. I did find a DVD plus a magazine. When the cashier was open a guy wanted to get two 5's for a 10, and the dealer wouldn't unless he bought something. Now I understand that's 7-11's policy, but with the cash register open anyway, would iut have really hurt the store to do that and create a bit of goodwill? He probably did get an extra sale this time, but I bet the buy passes on making a purchase at a 7-11 in the future as a result. Something that could have been avoided with a little Christmas spirit (the real type, not the buying type) and helping a fellow human being with something trivial to the sotre but helpful to the person.
You don't have to shout Merry Christmas! at the top of your lungs, but be cheerful. Make your customers feel happy to be out and about on Christmas Day.