One alternate to storing all of the values in the cart could be to have unique session variables setup that hold the values. Then at the end of the process you can reference these session variables when you store the info in the db. This way you could just add in more session variables instead of cart columns.
If you are going to have more than a couple of different items in the cart like this then it might get difficult to manage all of the session values. If this is the case you could have a temporary table in your db that you can insert to with the values, then you can store the inserted id in a session variable as a reference. When you are finishing with the process you can add a recordset or multiple recordsets to your pages and filter on the session variable that holds the id.