Closest thing to a donut I can drink coffee out of
As far as foods that double as dishes, off the top of my head I could only thing of a bread bowl for soup. You could certainly drink coffee out of a bread bowl, but I don't think it will be enjoyable. 

A bit of googling leads me to:


http://www.fastcoexist.com/1680504/a-cookie-coffee-cup-thats-easy-to-recycle-just-eat-it


The trick behind this is that it's a cookie lined with "special icing sugar" that works as a semi-waterproof barrier and an insulator. It will dissolve over a long enough time, though, and will sweeten the coffee as it sits in the cup. I can't find any information on when it hits stores, but it's a Lavazza product.