This disclosure presents techniques for selecting an add-on item to present to consumers at a check-out user interface of an electronic marketplace. The selection techniques involve presenting a consumer with a selection of add-on items that are unrelated to items added by the consumer to her shopping cart. The check-out user interface can present the consumer with a one-time offer to add the add-on item to her shopping cart. In some examples, the add-on items can represent over-stocked items or items that a supplier is attempting to liquidate. Further, the selection techniques can minimize the additional labor cost of retrieving the add-on item from a fulfillment center, by selecting add-on items that are located within a close physical proximity to items that the consumer has already added to her shopping cart.