I've just emptied my compost bin and in addition to good quality composted brown stuff, I had various bits of plastic, a spoon, and nylon threads. Of the degradable matter, there were some pea-nuts, the nuts from avocados and bits of newspaper which had been used for mulching (I used too many sheets together and it turned to plywood).
This is after two years - one in a cone (on a concrete base to deter rats) and the second year in a tumble bin.
I still can't figure where all the nylon threads came from.