Well,you are asking a serious of module which certainly contains selection item, pricing, item deletion , total pricing and even credit card payment and many other things.But as you said you already done for a single item and I believe you included those things that I mentioned above. You are almost there and you need only making your logic to work with collection of items. Take a look at this DNN link that will give you insight.
DotNetNuke-Shopping-Cart[
^]
Submit an article or tip