Regardless of financial situation, you have to plan. Work out how much you want to spend on Christmas and put away equal amounts each month (or week) to achieve that goal. If you know you haven't put away enough, then you know you can't spend that much come Christmas.
Christmas doesn't have to be extravagant. Christmas is about love - not gifts. Handmade gifts are far more meaningful than shop-bought gifts. Christmas dinner doesn't have to have ALL the trimmings. You can jazz up a can of baked beans if it is all you have.
Christmas is what you make of it. Your enthusiasm for Christmas is infectious. Share your joy with your loved ones and they will feel the joy too.
Best wishes to all those who are struggling. Just remember - what you take away from Christmas is your memories, so make your loved ones remember a magical day regardless of your circumstances.