Sometimes there are parades and such on these holidays in the cities that you can view. Flag day I'm not really sure about, Columbus day is a bit controversial. There are parades but usually there are many protests because columbus was not a very good person. Independence day is most notably celebrated by evening parties with fireworks displays.

It is? haha, no one does anything on Flag Day or Colombus Day, I mean Flag Day is barely known and there are just sales on Colombus Day and they're federal holidays so schools, banks, post offices are closed...Independence Day=July 4th, fireworks all night everywhere and barbeques and partying and festivities :)