Cross-sell products are a great way to increase sales. For example, if you sell electronic toys, a quick easy way to increase your revenue per order is to remind the customer to buy batteries right before checkout. There are many cross-sell opportunities for almost every type of business. Many times, these are high margin products or services being sold to impulse buyers right at the last minute (e.g. insurance, gift wrap, etc.).
The cross-sell products are offered to the customer on the cart page right before they proceed to checkout. Therefore, when putting together your cross-sell products, think about what your customer will perceive at the moment before checkout. You want to offer one or two interesting products that are relevant to items in his cart at a small price tag relative to his total purchase. You definitely want to show a catchy title like "Don't forget your batteries!!!"
You must first enable the Cross-sell products feature under Configuration > General. Once enabled, you can offer cross-sell products such as batteries that are targeted to a few specific products you sell under Catalog > Products menu or you can offer products that are generally available to every product such as gift wrap under Configuration > Cross-sell product settings.
Revindex Storefront has a powerful rules engine that allows you to optimize your cross-selling effort by showing only qualified products that are relevant at the point of checkout. For example, you can offer $5 batteries when you detect electronic goods are purchased in the cart with missing batteries and his total purchase reached at least $40. You can even pair it with a promotion to entice your customers with a discount like "This product is offered only to you at 50% off because you spent over $100". Whatever the products you decide to offer, it should always make sense and add value for the customer.