I would like to have a set of cards that tell me what expansion sets are in play. There would be 9 cards, and on each card would be the picture that identifies an expansion set ( http://www.arkhamhorrorwiki.com/Expansion ). For Kingsport, a lighthouse with a beam shining down and to the right; for Dunwich, a barn and a chimney; for Lurker, a Lurker. All nicely drawn full size cards with colour artwork, but recognisably the same image that's used as the icon on the cards from the expansion set. I'd put the cards for the expansion sets in use across the top of the board, face up, and the rest in the box. Then it would be easy to quickly compare the icons on the card you've just drawn (from whatever deck) to the pictures representing the current game, and discard the card if it has anything that isn't being used.
Some of these pieces of artwork already exist—the Eye of Horus (for Dark Pharaoh) is already on the backs of the Exhibition encounter cards. But what about the rest? Is there a good picture of a goat's head, an anchor, or a book? Or do these pictures only exist in tiny black and white form?