I wouldn't put in anything which can continue to grow in the compost - no roots, no things like ivy which root as they go along. I wouldn't put in bindweed, and I've not sure how quickly pine needles break down. Probably not.
I don't put in anything woody, or rootballs of pot plants. Be warned if you put in old tomatoes, melons or potatoes, that they will grow like the clappers as soon as you pot up the new compost - we've had a fine crop of self-grown tommies this year in the pots with the primulas!