Choose one or more of the following offbeat holidays to include in your stories. Maybe because of you and what you write, the little-known holidays you select to write about will become popular to celebrate.

National Tongue Twister Day - This is day to see just how many tongue twisters you can successfully say, then maybe make up one of your own.
You could make a tongue twister the basis of your next story. You could use one of the familiar ones, such as Peter Piper, or you could use one that isn't so familiar, such as Denise sees the fleece. You can find 524 English tongue twisters at this site - http://www.uebersetzung.at/twister/en.htm.
National Young Reader's Day - This is a day on which we are supposed to show just how important reading is to our young people. I would just buy the young person in my life a really good book then read it with him.
Fibonacci Day - a day for all math lovers to celebrate. It is celebrated on 11-23 because 1,1,2,3, are the first four numbers in the Fibonacci sequence. What is the Fibonacci sequence? In this sequence, the next number is found by adding together the two numbers preceding it. 1+1=2, 1+2=3, so the first four numbers are 1,1,2,3. The next number would be 5, because 2+3=5.
You could write an entire fiction series of books or stories around numbers. The television show Numbers was extremely popular.
Birthdays of Television Characters and Famous People
Cookie Monster's birthday
Mickey Mouse's birthday
Tweety Bird's birthday
Doctor Who's birthday
Charles Schultz's birthday
Mark Twain's birthday
Writing Holidays
National Author's Day - This is a day set aside to show your favorite author just how much you appreciate their writings. I would suggest sending your favorite author an email or a letter conveying to them just how much you enjoy reading their books and how eagerly you await the release of the next one. Another way to celebrate would be to go out and buy a book by this favorite author and give it as a gift to a friend.
What if your character had a chance to meet his favorite author on this day? What if your character just happened to have the personality of a stalker? What if your character decided that it was time for his favorite author to personally teach him how to write books that would sell?
Cliché Day - On this day, try to make everything you say a cliché.
This would be a great day to create a character who always speaks in clichés. No matter what he or she says, whether it is about cooking, reading, paying the bills, or whatever else, this characters always uses at least one cliché in what he says.
I Love to Write Day - I think it is pretty self-explanatory how you should celebrate this awesome day. Will this be the day you finally finish your first novel or story? Will this be the day you decide that writing will be a career for you?
You could write a story about a person who has always loved to write but has never taken the time or made the effort to write a story. On this day, however, this person is challenged to do just that. How does it turn out?

