On days when you have abbreviated class meetings or when you will be out, it's always difficult to come up with new and engaging activities to do without instruments.
I have been listening to NPR's "Tiny Desk Concerts" on my commute lately, and I stumbled across their concert featuring Flor de Toloache, an all-female Mariachi group. All of my classes are working on a Mariachi song for our latin themed concert in November. Today I gave them some information about Flor de Toloache and its members that they could complete while watching the concert. You can download the worksheet below the video.
Other podcasts that are music-related:
Soul Music (BBC Radio): Takes pieces of music with "powerful emotional impact" and discusses the background and history of the song. Songs range from classical to broadway hits.