My first Carina release, The Sergeant's Lady, is set with the British army on the Iberian Peninsula in 1811-12. Though my story's timeline skips over Christmas, given that it's December now, I decided to make my inaugural post about how Wellington's army observed the holiday.
Christmas hadn't yet become the lavish production it is today even among those safe at home in Britain, but the officers of the army in the field entertained one another with the best dinners that could be obtained. In 1812 two turkeys formed the principal part of the holiday feast for Wellington and his guests, while one year a group of artillery officers had "soup, salt fish, roast beef, boiled beef, mutton, vegetables, etc., etc., and a remove of turkey, fowls, ham and tongues--afterwards pastry." After dinner they lived up to the hard-drinking standard of the times with toasts to "All absent friends, the King, the Prince Regent of Portugal, to England, to Lord Wellington, and the British Navy, to name only the principal toasts."
In 1810 some of the officers even had something that would've been all but unheard of in England at the time--a Christmas tree. As many of you may know, Christmas trees got their start as a German custom and didn't become generally popular in Britain or North America until the Victorian era a few decades later. But the British army of the Napoleonic era included a King's German Legion composed of Hanoverian troops (since at that point the King of England was also the Elector of Hanover, which is now part of Germany). And the officers of the KGL kept up German tradition and had a tree--a lemon tree, decorated all over with oranges and candles.
So much for the officers, but what about the enlisted men? We don't have as many records, because so much of our source material is officers' correspondence and diaries. But we know that in 1812 the colonel of Gordon Highlanders ordered his company commanders to "give their men as good dinners as they possibly can tomorrow...as it is Christmas Day," and Captain John Cooke of the 43rd Light Infantry provides the following description of Christmas Night, 1813:
Just before dark, while passing a corporal's picquet, an officer and myself stood for a few minutes, to contemplate a poor woman, who had brought her little pudding, and her child, from her distant quarters, to partake of it with her husband, by the side of a small fire kindled under a tree.
For all of these details I'm indebted to Antony Brett-James' Life in Wellington's Army. If you're writing about the Peninsular War, or even just writing a hero with the war in his past, it's well worth getting from interlibrary loan or hunting down a used copy (generally cheaper on abebooks than Amazon, incidentally).