Ding ding ding! Here is a photo of a cigarette packet included in a Christmas box sent to every BEF (British Expeditionary Force) soldier in France in 1914. You can see that the back offers quite a lot of room for writing:
That Christmas box itself, by the way, is beautiful. Brass, with an embossed portrait of Princess Mary, and scrollwork on the cover. My former father-in-law had one, that had been brought back by his father from France - missing, ironically enough in the context of this conversation, only the cigarettes, which he didn't smoke, but used in trade.
https://britishmilitarybadges.co.uk/products/princess-mary-1...
That Christmas box itself, by the way, is beautiful. Brass, with an embossed portrait of Princess Mary, and scrollwork on the cover. My former father-in-law had one, that had been brought back by his father from France - missing, ironically enough in the context of this conversation, only the cigarettes, which he didn't smoke, but used in trade.