1. A system for providing discounts to products purchased by a customer at a retail establishment, comprising: a list of the products to which discounts are to be applied; a computer system provided with a memory containing said list of the products, a discount amount applied to the products included in said list, the expiration of said discount amount, as well as the retail value of the products included in said list; at least one checkout station in communication with said computer system, said checkout station including a first terminal for entering information relating to products purchased by the customer and a second terminal provided with a reader/writer device; and a card retained by the customer, said card provided with an interface device and a memory, said memory initially programmed with a first monetary amount from which discounts based upon the products purchased by the customer are deducted, said first monetary amount read by said second terminal, said second terminal writing a second monetary amount into said memory reflecting the discount applied to the products purchased by the customer based on the information included in said computer system.