Buy a big bag of regular popcorn kernals. Then pop them using a hot air popper, or maybe the microwave. Biodegradable as well, or use as bird/squirrel feed by receiver. See links:
http://www.communitiesbychoice.org/printme.cfm?ID=235&print=1
http://palimpsest.stanford.edu/byorg/abbey/an/an16/an16-2/an16-201.html