Zen Cart Coupon Auto Add allows you to specify items to automatically add to the cart when a particular coupon code is entered. It's good for adding free gifts, or automatically adding Better Together, Extended Family, or other product pairings or groupings.
Items which are set to Coupon Auto Add must be able to be added to the cart from a normal listing page. For example, if you search for the item, the search results page shows the item with "Add to Cart" functionality and not a "More Info..." link). What this means is:
For more information, please visit this product's webpage.