I have two Kings Island ash trays from about 1974; both of which my wife bought at Brown's Market Antiques in Hamilton before the start of the 2009 season. I had them on KIC, but the post was apparently archived. They are the size and shape of medium-sized dinner plates, and have little 1/2-inch tiles of different colors going around a printed picture of the park in the center (complete with the Sky Ride). If I can find what i did with the pictures, I'll post them back on here; they were really well-preserved (never used as ash trays, but more as display plates it seems).
I also have a yellow "Gilligan" style hat from Paramount's Kings Island, circa 2003, two Diamondback "first rider" shirts that have never been worn (I was actually like, rider number 5200), and an "Italian Job Stunt Coaster" shirt from 2005, and a plastic photo "viewer" key chain from last season.