Sorry if this has already been suggested, but how about a Ninja Vs Pirates one or Harry Potter-type?
So like eye patch, hook, ship background, treasure chest, gold dubloons, pirate hat, pirate clothing, ninja costume, ninja and pirate weapons, nighttime rooftop background (for ninja)
Then broomstick, potion bottles, spell book/spell book stack, wand, House Shields (but non-Potter Houses), dorm background and other HP-style items.

I know we have lots of Halloween items and owls and cats and rats, so they would go with the wizardy stuff.