A pep rally or pep assembly is a gathering of people, typically students of middle school, high school, and college age, before an event. The purpose of such a gathering is to encourage school spirit and support.
You can solicit support from staff and students to participate in a skit, role-play, song, cheer, flash mob, etc. at a rally. There are endless creative possibilities.
Need some ideas? Google “pep rally” and you will find many examples.