If you leave the Grim reaper's house with this item, the message "The Halloween items vanish. You feel a little strange." will show in the chatbox. This message also shows up if only one item is held when leaving.
In addition to the obvious use in the quest, drinking the Moonshine prior to turning it in will result in a brief transformation into a werewolf.
You could create an offer for "Ingredients" on the Grand Exchange, although they were unobtainable. The reason for this is currently unknown. This was later fixed and now anyone who put up an offer to buy it was given a refund of coins. It still showed the picture of the moonshine ingredients, though it now says "null" instead of "Ingredients".