Edit Sizes & Custom Fields on Cart summary page

At the moment the first step of the checkout process (checkout page) doesn't let the customer edit the cart without selecting a line item and then going back to the product details or designer page. 

It would be nice to be able to select a line item and have the ability to update Sizes, Custom Fields, and duplicate the line. If a line could be duplicated it would also be nice to have the ability to change the product's color.