Here is a link to Apples4theTeacher. Along with the usual worksheets and word searches they have also included a short bibliography of books about community workers. This might be exactly what you were looking for to trigger a student's interest. http://www.apples4theteacher.com/holidays/labor-day/kids-books/ Labor Day is always celebrated at the First Monday in September.
In 1776 a small group of colonies declared their independence from England and it's king. At that point they had to begin planning how they would govern themselves. The Constitution established the framework for the management of our nation and the laws to protect the citizens that live here. September 17th is Constitution Day. Here is a good website that helps explain what the Constitution, Preamble and Bill of Rights are all about.
At the 11th hour of the 11th day in the 11th Month of the year 1918, the First World War ended. This date is still honored in the United States as Veteran's Day. Here is a link from TeacherVision to a grade level appropriate set of facts and information about Veteran's Day. http://www.teachervision.fen.com/veterans-day/history/3204.html?detoured=1 The Veteran's of Foreign Wars VFW also a good resource, especially if you would like to have an actual Veteran speak to your class. More information will be provided.
Here is a website from the California Department of Education with some ideas and standards alignment for activities related to the Cesar Chavez Day of Service; http://chavez.cde.ca.gov/ModelCurriculum/Teachers/Lessons_K-3.aspx In California Cesar Chavez is honored, not with a day off from work, but rather by taking the opportunity to perform service in the community. The date remains the same, March 31st, each year, the anniversary of Cesar's birth.