We have days set aside devoted to different events such as St. Patrick's Day (to honor an historical figure we celebrate the demise? I'd heard this was the say he died. Or is that just the ase with Saints?). We have more local holidays such as Independence Day on February 4 (dedicated to our country's freedom) and Thanksgiving (the first party in the New World [i.e., the United States]) and Bastille Day on July 14 (the French symbol of the monarchy's end and the beginning of the First Republic).
If you're worldbuilding, holidays can sometimes help to move the story along and provide a plot point, depending on the action. If you're not worldbuilding but instead writing reality-based fiction or nonfiction, if action takes place during a holiday it will have some effect upon the action.
If you're writing a fictional piece right now, then what would a holiday celebrating your character be like? What would be the point of the celebration? If non-fiction, then choose someone very important to you, whether historical or contemporary, to create a holiday for; why would you create the holiday? What would it celebrate, and why?
Regards,
Elizabeth Anne Ensley.