Since the cart just holds a collection of items that have been added there is really no concept of related items within the cart other than columns having like values. You could add in an extra column to the cart that would hold an identifier value so that you can relate some items to another based on the value in this column.
Even if you have the items organized like this there is no functionality to reorganize the cart display based on the relation of the items. If you want to get this implemented it would be completely custom and would require a bit of hand coding and editing of the eCart code.
