Another option would be "overnight oats". I've never tried this, but a quick Google will show everything needed to know about this alternative.
I also make keto Flaxseed Cinnamon bun muffins sometime and easy go to when prepped (recipe is from The Keto Diet: The complete guide to a high-fat diet, By: Leann Vogel – it has wonderful recipes even if you're not doing Keto!)
Hope this helps 😊!
Plain Greek yogurt
Granola, or oats
Mashed up bananas
This part's obvious, but you can set certain coffee makers to brew on a timer as well.
However, some foods that are commonly used for pre-prepped breakfasts that I would know of off the top of my head would be oatmeal, yogurt, quiche, fruit and berries.