Sci-fi a fantasy

Eric is the Discworld's only demonology hacker. Pity he's not very good at it... All he wants is his three wishes granted. Just the usual: to be immortal, rule the world and have the most beautiful woman in the world fall in love with him. He wants to call up a tractable demon. But what he gets is Rincewind, probably the most incompetent wizard in the universe, and the extremely intractable and hostile form of travel accessory known as the Luggage...