Gilly Weed Keep the potion bottle theme going with this bottle of Gilly Weed ($10). Used by Harry Potter himself to breathe underwater during the Triwizard Tournament, any Potter fan would love to have this as a souvenir after a witchy Halloween party. PS: don't try the Gilly Weed at home; it's for decorative purposes only. Image Source: etsy.com Gilly Weed $10 from etsy.com Buy Now