A system and method for grouping and selling products or services using a computer system, potentially connected to a network. The computer system includes a computer with multiple terminals, potentially instantiated as a server computer or computers and distributed client computers. The computer system presents a sales interface on some terminals. The sales interface shows products or services and groups of products and/or services that are for sale. The computer system presents a back end interface on some terminals, which can be used to enter new products, services and groupings of products and/or services to be offered for sale on the sales interface. Descriptions of the products or service offerings are entered into the computer system either by data entry operators using the back end interface or by a program reading product or service descriptions from external computer systems. The method groups these products or services according to an affinity algorithm. The groupings may then potentially be reviewed and approved or selected by human operators using the back end interface before being offered for sale on the sales interface. One advantageous application is the dynamic packaging of perishable items such as travel goods and services (e.g., airline tickets, rental cars, hotel rooms, entertainment opportunities, etc.).