Embodiments of systems and methods described herein provide users with access to a weight-based shipping service that enables the users to purchase a group of items and pay a flat shipping fee. These systems and methods can enable a user to combine certain items into a box or set of boxes based on weight for a reduced shipping cost. In addition, systems and methods described herein can recommend items to users for purchase based at least in part on the items that a user has added to a box, including based on remaining weight in the box.