Stores remain open because they ensure somebody isn't on vacation and thus able to work. They sometimes give extra pay if you work a holiday (this is rare though - generally there is somebody who wants the hours/pay more than this holiday off - they can take time off a different day).
For small business (think a plumber) it is common to arrange a competitor who will take care of your emergency customers needs.
Stores remain open because they ensure somebody isn't on vacation and thus able to work. They sometimes give extra pay if you work a holiday (this is rare though - generally there is somebody who wants the hours/pay more than this holiday off - they can take time off a different day).
For small business (think a plumber) it is common to arrange a competitor who will take care of your emergency customers needs.