By the package design problem we are given a set of queries (referred to as a query log) with each being a bit string indicating the favourite activities or items of customers and required to design a package of activities (or items) to satisfy as many customers as possible. It is a typical problem of data mining. In this paper, we address this issue and propose an efficient algorithm for solving the problem based on a new tree search strategy, the so-called priority-first search, by which the tree search is controlled by using a priority queue, instead of a stack or a queue data structure. Extensive experiments have been conducted, which show that our method for this problem is promising.