An acrostic poem uses the first letter of each line to spell out a word.
You can find examples of Merry Christmas acrostics on the internet, but do not underestimate the challenge of writing an acrostic poem.
At a simple level, try writing the word down the page, then getting students to supply one word associated with Christmas for each initial letter. For example, for "m" they may suggest mistletoe or mince pie.
More able students could use each letter to suggest a verb, for example "make". Then they could complete a sentence, such as "Make the Christmas cake". They will end up with a set of lines describing various Christmas activities and some students could then rejig these lines into a poem.
The poem Christmas Bells by Henry Wadsworth Longfellow starts out like a conventional poem talking about the message of peace on earth and goes on to ask how this could apply to a world at war. At the time, his own son had just been injured in the American Civil War. (A background piece with more details by Robert Carroon can be found on the internet.) There are obvious links to the present day, with British soldiers in Iraq and Afghanistan. Working in pairs, students could imagine a correspondence between a father at home and son at the frontline.
Personal writing (diary)
In 2004, The Observer's Scottish edition carried an interview with a soldier who remembered the Christmas truce in the trenches in 1914. The article was written by Lorna Martin and it is on the internet.
It is perhaps a bit too long for most basic skills students to read, but my students love being read to. Read it aloud and then ask them to write the soldier's diary entry for Christmas 1914, and perhaps Boxing Day, when fighting resumed.
In 1987, a child named Virginia O'Hanlon wrote to The New York Sun and asked the editor "Is there a Santa Claus?" His reply was printed in the newspaper. You can find copies on the internet.
There is a lot to discuss, such as the style of the reply and the innocent trust the child had in the editor's opinion. You could ask students to identify the main point in each paragraph. They could consider what they would say in the editor's position, note down the critical points they would make, then construct their own response. They could write it up or just do it as a speaking and listening activity.
Find or write step-by-step instructions for making a decoration. Chop up each step and ask the students to reassemble them. Then give them the materials to make the decoration.
Alternatively, let the students work in pairs, but back to back. One student has the instructions and reads them out. The other students makes the item, but without being able to see the instructions or diagrams.
Some supermarkets have free magazines with stories, ideas for decorations, presents and recipes, all of which can be turned into reading, writing and speaking activities.