There is very little about writing fiction that I do not find 'fun'. I like using my imagination, and fiction lets you do that a lot. One thing that I have to think about when I'm writing science fiction is to not forget the holidays. (Holidays come up in other types of fiction, too, and must be thought out carefully.) Just for an instance, suppose I am writing about a new colony on an undeveloped planet. The colonists have some supplies and equipment, but still must depend only on what they can do themselves in order for the group to survive. To me, it makes sense that they would find some reasons to take a day off, a chance to play and celebrate whatever progress they've made. A day to remember why they are there. And some of those festival days would continue, even after the colony and culture has matured and the 'need' for such opportunities to forget their worries has waned. What would those early holidays celebrate? What would they be like a few generations later, when the culture has matured?
Since I've just cooked and eaten our traditional Thanksgiving dinner (and am in no hurry to clean up the dishes), I'll examine that type of holiday today.
Long ago, before the pilgrims came to North America, it was pretty traditional in Europe to feast and 'party hearty' in the autumn and early winter. The easiest way to store an abundant crop was to fatten up the people with most of it. Otherwise, fruits, vegetables and grains might rot and be of no use to anyone, and people would be very hungry in deed by the time any springtime foods became available. To my thinking, Americans still tend to do that, and I have a tendency to have my Colony X do the same. Maybe they don't need to store their crops as body fat, but I think it makes sense for a group that depends on agriculture to celebrate an abundant crop by having a party. So yes, my Colony X would have a Thanksgiving-type holiday. And it would probably continue even after most of the population is no longer involved in growing food, because by then, it would be part of the colony's tradition. Would they have pumpkin pie? Maybe not pumpkin, but they would have something made from local foods.