This addon shows an Xsell (Cross-Sell) box on the shopping cart page. It's based on the Xsell addon and the Modular Shopping Cart BS Addon. All of this requires osCommerce Responsive (Bootstrap) version 2.3.4r Gold or later.
The module uses products that have been selected for cross-sell on the product(s) currently in the cart. The maximum number of products shown can be set, and the order in which they are shown (popularity or random) can be set.
Support thread: http://forums.oscommerce.com/topic/409352-xsell-in-cart-for-modular-shopping-cart-responsive/