E-Commerce best approach?

I’m creating a E-commerce site and having some trouble with my approach for design. Basically what I want is for each customer will pick what they want to buy and have the opportunity to put it into their own custom packages for a discounted rate. The items will change on a weekly basis and I’ll have to administer that and I would like it to be as easy as possible for me. I guess what I’m asking is how do I do this using Drupal?