More formal or mystical CR rituals are often based on traditional techniques of interacting with the Otherworld , such as the act of making offerings of food , drink and art to the spirits of the land , ancestral spirits , and the Celtic deities . More formal or mystical rituals are often based on traditional techniques of interacting with the Otherworld , such as the act of making offerings of food , drink and art to the spirits of the land , ancestral spirits , and the Celtic deities .