There are several traditions associated with Memorial Day. Various groups place flags on the graves of veterans. I appreciated that the Boy Scouts of Armstrong County Pennsylvania do that for Andrew McKee.
Communities have parades. I went to one several years ago where veterans marched, tanks were driven down the street, and many community groups paraded with their floats decorated in red, white, and blue.
Since Memorial Day is considered to begin the summer season, many people celebrate with a picnic. I do not picnic, but I do like to go to Greenfield Village, where they have the Civil War Remembrance. Reenactor soldiers camp out during the weekend, platoons march, and the calvary rides their horses. Historians present information on topics from armaments, to clothings to medicine.