There are three core elements of a Rhéhixan harvest festival, all under the umbrella title of "The Holy Sacrifice".
The Offering
The most central element, which is seen across the entire Rhéhixan population, is the burning of the first batches of everything grown. They believe this will help ensure a bountiful harvest the next year, as well, and will allow them to continue existing within the realm of the divine. So, each and every year, the first vegetables, grains, and other crops are gathered together and burned in a great village fire. It is important that the first harvested items are burned, and not the second, third, or (heaven forbid) the last, in order to show goodwill and hospitality toward the divine.
Prayers Over the Dead
Over the village bonfire, a local elder or elders will recite prayers on behalf of all souls who had died the previous year, so that they may rest in peace until the end of days. If there are any particularly recent deaths, this is the time to bury those bodies, but for all other times of the year, the body should be buried as expediently as possible.
The Festival
Following both of these steps, the fun may now commence. In the orchards there are contests such as bobbing for fruits. Divination is common, as well, especially for matters such as how the next year will go and if a given individual will find love. If there are bad crops that year, one may lob them at one's enemies' homes, rather than simply letting them go to waste.
There is also an element of role-reversal, or at least of lifting of social constraints. Running freely about and causing light mischief is permitted, and if in the course of such activities, one's veils or clothes come loose, this is not considered a sin. This is also the one time of year where it is permissible to brew and consume grain alcohol (excepting a particularly thick brew that is always permitted year-round, in case of bad drinking water).
I love the different elements here. The offering of the first harvested crops is such a good idea, and makes sense. Kind of like feeding a guest first. I also like the aspect of role reversal and light mischief that's permitted. That's a fun detail. :D
I've never directly went "these are X in space" with anything (except the article I wrote on Christmas, but that's on purpose and follows yet another real-world trend of important people influencing the popularity of certain things), but I do read books and know things, and sometimes I like to add little patterns I've found to my world.