I like to make up holidays.
The date of Bahamut's birth, or perhaps the day of the birth of his first children with Tiamat. The chronicles are unclear and the dragons aren't clarifying.
It is said that Bahamut has a child who poses as each of the races (yeah, player races). This holiday, for non-dragons tends to be about them, asking them to speak to their father on behalf of said species and see to their empires becoming strong, children smart/cunning/powerful.
It is a day of gathering, usually families stop working for the day and go out into the fields or the forest and find things to give to their loved ones. At night, there are hot, mulled beverages and the giving of gifts, always found during that day. The Dragon-born are said to draw the holiday out over twelve days of searching and twelve nights of gift-giving, making the process far more complicated.
Among Tiefling crime families in urban areas, the -found- items are often stolen. Peoples have different takes on the holiday in different places.
The Night of a Thousand Ravens:
This is the night in which the Raven Queen herself sees to each of the dead personally, as her servants are given the night to their own pursuits. Ravens flock the streets, imitating people and stealing shiny bits. Angels with black wings are said to seek romances forbidden on any other night, leaving half-angel children who can talk to the dead in their wake.
Those who are on death's door get a visit from the Raven Queen herself and those who choose to, may die silently, with dignity. Orcus cults are known to hole up and hide during this holiday, not wanting their murderous ways to draw her attention. Occasionally, a high level servant will attempt to murder someone dear to the Raven Queen, in an attempt to draw her out and ambush her. This has historically not gone well for them. Groups of ravens are called an unkindness for a reason.
Wall and Glade Festival
This festival takes place in one of two places, either on the edge of a city, where you can see both the city's walls and the natural surroundings beyond or a natural park within the city.
In this festival, the two women are joined in marriage, with the high priestesses from the temples pf Erathis and Melora representing their goddess in the flesh. Sometimes couples who are made up of one person from a city and another from the country are married at the same time.
When the festivities are rowdy enough, the boasting begins, with each priestess declaring their own goddess as superior and how they will go about defeating the other, overrunning the city with vines or expanding the walls into the heart of the forest. Races, riddle-games and competitions of friendly martial prowess occur between the country folk and city folk until the wee hours.