I look at so-called holidays in my country. Instead of 4th of July, I call it Liberty Day and set the activities for such. And, yes, fireworks are included. :) I also added Labor Day (no name change) as the first Monday in Fall. I use MCCC and give the school-aged Sims the summer off. Then they resume the day after Labor Day. I have also followed what another player said ages ago. That player devised a way for their Sims to go to church. The only activity is to attend the service. (You could easily make it any religious service of your choice. It's a rabbit hole.)
But there seems to be a plethora of National days of … you fill in the blank. I really hate it when National Ice Cream day falls on a Fasting Day. So not fair, LOL.
Let your imagination go wild. I love this calendar feature, myself.