Here's a website that lists all the official, quasi-official, or just plain weird celebratory and commemorative days in the year:National Day Calendar
Every date has multiple entries, so you should be able to find a special day for just about anything you want to celebrate. The explanatory page for each entry includes the commemoration's origin. Some that aren't official holidays have been established by individuals or organizations, while for others the website says it's still "researching" the source. In other words, they don't know. Since apparently anyone can register and add a day to the calendar, it's possible some of these "special days" are simply things made up by people who thought they would sound cool. They're fun to contemplate, anyway.
Here's a page on the history and possible origins of April Fool's Day:April Fool's Day
These are just a few of the many "days" listed for this week in 2021, in addition to April Fool's Day and the Christian observances of Holy Week events: March 29 -- National Nevada Day, Lemon Chiffon Cake Day, Mom and Pop Business Owners Day, Vietnam War Veterans Day. (I suspect this last one is real for sure.) March 30 -- Take a Walk in the Park Day, I Am in Control Day, Virtual Vacation Day (probably a new invention for the current situation). March 31 -- Bunsen Burner Day, Clams on the Half Shell Day, Manatee Appreciation Day (founded by an organization dedicated to protecting endangered marine animals). This year April 1, April Fool's Day, is also dedicated to sourdough bread and burritos, as well as the regular annual National Take Down Tobacco Day, whose exact date varies. April 2 -- World Autism Awareness Day and National Reconciliation Day, plus an occasion to appreciate ferrets and peanut-butter-and-jelly (presumably not together). April 3 -- National Chocolate Mousse Day, Find a Rainbow Day, and Love Our Children Day (always the first Saturday in April, according to the website). April 4 -- in addition to being Easter Sunday this year, it celebrates school librarians, newspersons, geologists, and vitamin C, among other entities worthy of recognition. It's also listed as National Walk Around Things Day. Well, that's preferable to Tripping Over Things Day. :)
I can enthusiastically support Chocolate Mousse Day, for one. As for today, it's also designated National One Cent Day. The website doesn't identify its origin, but they offer an interesting overview of the history of the U.S. penny, of which we keep a can-full in a drawer, as many people do:National One Cent Day
When my husband and I got married, in the mid-1960s, some gumball machines sold candy for one cent, and a retro bargain store near our first apartment carried a few items priced at a penny each. The value of a penny faded to essentially nothing long ago, yet we still understand what's meant by the proverb, "A penny saved is a penny earned."
Margaret L. CarterCarter's Crypt