The Scroll of Luck belongs to the Seven Lucky Gods of Nekonron, and is reputed to have powerful secrets hidden upon it;.
Stolen by Happosai, he traded it to a restaurants owners in lieu of cash by claiming it would bring them good fortune, and cause a prince to come and marry the woman who held it.
When the dissatisfied descendant of that family, Lychee, sought Happosai out and threw down the scroll, it coincidentally summoned the flying ship of the Seven Lucky Gods, whose leader, Prince Kirin, promptly abducted Akane Tendo under the mistaken belief that she was the bearer of the scroll. When this happened, Happosai claimed that the scroll held martial arts techniques that would allow the bearers to conquer the world, inciting Ranma, Ryoga, Shampoo and Mousse to give pursuit and rescue Akane.
In truth, Happosai had been lying in both cases. The Scroll of Luck is important to the Seven Lucky Gods because it contains a ritualized recipe for creating Fukujin Pickled Vegetables, utilized as part of the wedding ceremony for the Princes and Princesses of Seven Luck Mountain. It has absolutely no value at all outside of this ceremonial purpose.