Go Digital!
If you have access to technology, going digital is an easy way to keep a class near silent. Have students explore a digital composition tool like Chrome Music Lab (check out some of my lessons and activities for CML here), or have them play some music games on a website like 4four.io or musictheory.net to work on skills you are developing in class.
Research Project
If you find yourself out of your classroom and in the quiet zone for a few classes in a row, it’s a great time to get students to work on a research project. I love doing this project on the history of an instrument, or you can have students research a composer or song. If you prepare beforehand and print out research materials for the students, you don’t even necessarily need technology to make a research project work!
Worksheets
They’re a classic for a reason - and the great thing about using worksheets for a quiet day is you can prep them a long time in advance, and have them ready to pull out at any time if plans change and you need something on the fly. Change up the same old worksheets with some colour by code for recorder or solfege, or do some seasonal worksheets!
Book based lessons
Along with being one of my favourite things to leave for substitute teachers, book based lessons can be great for a quiet music day. Start by reading your students the book - or look on YouTube to see if there are any readalongs already posted if you are trying to save your voice! Then plan a coordinating activity - you can encourage students to go on a Listening Walk through the halls or outside, or choose any book with repetitive words and have students make a rhythm composition with them (I love having my students do rhythm compositions with colour names with the classic children’s book Elmer by David McKee, although you could do that activity with any colourful book!)
Review Games
A quiet day is also a good time to pull out some review games - not all can be played quietly but it can be a fun challenge in itself to play some silent bingo where you need to call bingo in a whisper! You can also try Scattergories - students love trying to be stealthy with their team so no one overhears their answers!
Hopefully one of these ideas gives you some inspiration for your next quiet music class day. Good luck!