When requesting an absence (eg vacation or sick leave), an employee designates specific dates they want off. For certain dates – public holidays – there's never any need to request off, and those dates can be omitted from an absence-request. (For example, if Christmas is on Tue and the employee takes off the whole week, then she needs to declare use vacation days for Mon, Wed, Thu, Fri but not Tue.)
T1. Allow administrators to create new activities of type "Public Holiday" (eg using "Contacts => New Activity")
T2. Allow administrators to list all "Public Holidays". Create a ReportInstance called "Public Holidays" (which lists activities of the proper type; if a time-filter is needed, use the current year). Add the "Public Holidays" report to the "Absences" menu.
T3. Add sample data for Public Holidays.