Materials for a group game or two. Lots of little prizes to win that fit your theme. A loosely scheduled list of activities that will help to keep the students on task. Have the students perform music that relates to the theme. Intersperse performance activity between music games, and let the students volunteer to play.
Required memorization is at the discretion of the teacher.
It may be necessary to have more than one party and group the students by age. Here is a very easy one that most of us have done. Many of us assign holiday music to our students anyway sometime during the fall season. Have the students dress up, or wear holiday colors. Christmas cookies and punch make great party treats.