There are actually some biodegradable packing peanuts made from (extremely) puffed rice.
I learned about these back when I was a network administrator in college. It seems we had some hardware shipped to us, and the box was filled with these packing peanuts. One of the other admins told me they were edible. I told him he was full of shit, up until the point at which he ate one.
Being an adventurer, I grabbed one, and put it on my tongue. When they get wet, they get sticky and their structure severely weakens....even developing a pasty texture. I ate it, and proceeded to eat quite a few more before developing a headache. It's not a good idea to eat too many packing peanuts.
I will admit, they certainly had a unique taste.
I'm a styrofoam packing peanut, and he's going to eat me!