Happy late Fourth of July to those of you who celebrate! I sincerely hope you all still have as many fingers as you started with. Naturally, the recent holiday made me think of how to create and celebrate the holidays in the worlds I'm building, and how they would look to outsiders.
For example: Between the ages of eleven and fourteen, my family and I lived in a Naval station in Spain. We lived "off-base", in a gated community where several houses had been leased by the US military and the rest of the community was made up of local civilians. On the Fourth of July, the only place where anything was really happening was on the base itself, as the day wasn't any kind of holiday to the rest of the country.
My father was never a big fan of crowds, and we knew that the base would be filled to the brim with homesick Americans watching the fireworks and listening to "God Bless America" while hoisting their beers. Instead of going on base to celebrate with everyone else, we decided to make use of the fact that our house had an accessible roof. (The way the houses in our community were built, the roof was the closest thing to a yard any of us had, so everyone used them for clotheslines and some gardening.) I just remember being on the roof with my family, watching the fireworks from the base, and noticing the other Americans on their roofs doing the same. It was a much calmer way of celebrating what can be a very boisterous holiday, and remains my favorite way to celebrate.
In general, societies use holidays to reinforce some kind of unification among their people. It's a great way to take a moment and reflect on what's important, and an excellent way of defining "what's important" to the masses. I feel like a world is incomplete without some kind of celebratory event that happens regularly. Now, I don't mean that every fictional society has to be like Seanan McGuire's wonderful Aeslin mice, in which anything can be a holiday, but it helps to have a few events that are commemorated in some way. In the world I'm working on for Camp NaNo this time, there's a Unification Day, celebrating the day the final treaty was signed and all of the territories fell under one ruler. For some of those territories, this is a day of great celebration; for others, it's a reminder of the freedom they lost when they were conquered.
Not everyone celebrates the same holiday the same way, so it's another good way of getting inside the heads of your characters. How do they celebrate Christmas? What are their favorite and least favorite holidays? You may never actually put it in a book or story, but it's another one of those things that helps flesh out a character and a world.