We have discussed here recently about using the whey from Mozzarella to make ricotta.
We have talked about uses from the leftover liquid from making yogurt.
We each have things for which we like bacon grease (or 'bacon oil' as Emeril calls it).
Many of us put the cut off parts of veggies in a stock pot or in a freezer bag for later making stock.
I use turkey carcasses (but not ones from smoked turkeys) for posole or other soup.
I used to get the remains of fish that had been fileted at the grocery, but so many of us wanted them that the price got too high for me.
I recently made some miso soup. I had the kombu I'd cooked in the dashi and the water I used to soak the wakame. Are either of those useful? I think I might chop the kombu and put it and the wakame water in my plants unless there are better uses. I have heard, for instance, about Kombu no Tsukudani but I have never made it; that would use the kombu. But hasn't the flavor already been cooked out?
What about water used for soaking other things such as beans?
Other than compost, what other things others might discard do you use and how?