A computer program product for prioritizing order fulfillment at a retail sales facility, including the steps of: a) receiving purchase request information at a retail sales computing device that includes identifying information and order information for the first customer, b) receiving location information for the first customer, c) processing the received location information for the first customer together with location information of the retail sales facility to predict an estimated time of arrival (ETA) for the first customer at the retail sales facility, d) scheduling a time interval for acquiring updated location information for the first customer, and e) placing the identifying information, order information and ETA for the first customer in an order fulfillment queue for all current customers. Entries in the order fulfillment queue are ordered in increasing ETA order, whereby order fulfillment activities can proceed according to the order of order requests in the order fulfillment queue. ETA is continuously updated for each customer, and thereby the order for fulfilling customer orders in the order fulfillment queue. For example, if a customer's distance from the retail sales facility increases (for example, due to a mistaken turn), that customer's order will drop to a later-served position in the queue. The location information for the first customer includes GPS-based location information of the first customer that is captured by a GPS device associated with a mobile computing device of the first customer. The location information for the retail sales facility includes GPS-based location information of the retail sales facility. The ETA prediction is performed using the GPS-based location information of the first customer and the GPS-based location information of the retail sales facility.