It wouldn't fit the theme, but maybe some materials from your A Dirty World stuff. Also preview AP games are always a great prize.
Also I don't know if it's been done before, but maybe a commentary track, or commentaries in the game materials from the original playtesters. Like anecdotes of how they felt at certain points, how wrong they were about certain decisions or about where they thought the game was going, or how creeped out they were at a certain point (i.e. Tom with the Bird in the cage in Lover In The Ice), etc. etc.
So stoked that this Kickstarter has done so well. Can't wait to see what else Hebanon Games has in store.