Hide different ingredients to a "potion" and make clues to find them.
Have the kids separated into teams (houses work best). Explain to them that there is a very important potion that needs to be made but the ingredients are nowhere to be found. Give them the first clue and it is basically a typical scavenger hunt. The first team to find all the ingredients, mix them up, and name their potion wins house points or another type of prize.