One of the most important and under-utilized features of any online store is the Wishlist. With Wishlists, customers can save items which they may not have an intention to purchase at the time, but that they find intriguing and may want to purchase in the future. After adding items to their wishlist and returning to your store, rather than having to search through your entire catalog to find the items they were interested in, they simply click into their wishlist and have it all available to them, ready to add to their cart.
Imagine this scenario: While browsing your store, Tom finds the perfect T-shirt that he's been looking for, and adds it to his shopping cart. However, a few other items catch Tom's eye. Since Tom's never ordered from you before, he wants to make sure the size he's ordering will fit correctly, and goes ahead and only orders one shirt from your store. Two weeks later, Tom realizes that he really likes the T-shirt he ordered from you, and it fits perfectly! Tom returns to your store to order some of the other items that he liked, but he can no longer locate them. Tom is very busy and doesn't really have time to find these items again. Tom leaves your store without making another purchase.
Tom is browsing your store. He's already found the perfect item that he knows he's going to order today, but there are a few more items that he likes. Before ordering too many T-shirts, Tom wants to make sure it'll fit right since he hasn't ordered from you before. For each of these items, then, Tom clicks the little heart button that adds the items to his wishlist. Tom proceeds to order his one item today, and receives it two weeks later. He loves it! Tom returns to your store, clicks the wishlist button, and all his heart-ed items are right there! Tom adds them to cart and proceeds to make his second (and much larger) purchase with your store.