If you're teaching The Great Gatsby by F Scott Fitzgerald, you'll want this simple assignment that can work as group work and group discussion. Use it before you show all or part of any film version. Students make decisions about character type, then find a quote to back it up, and finally cast a Hollywood star for the role.
It might be useful to print a list of current stars' names in order to avoid students who claim to not know any actors' names. Being in groups should allow you to avoid some of these concerns, too. If you live in Canada or somewhere where students never see movies, you can change it to school staff members as the cast.