there is no documentation for doing this that I can point you to.
you would need to create 2 tables in your database.
the first table will have a primary key column, another column to store the ID of the logged in user, and a text column to store a name for the saved cart.
the second table will have a primary key column, a column that relates the ID column from the first table and additional columns for each of the columns in your eCart object. for example:
cartID - primary key
cartUser - relates to user.userID
cartdetailID - primary key
cartdetailcartID -relates to cart.cartID
cartdetailProductID - stores the ID column of the cart
cartdetailProductName - stores the name column from the cart
on the page that you add the Save Cart button, add a textfield to set the name of the cart.
then use the eCart Store Order Summary behavior to create a new record in the cart table for the order. bind the cartUser column to the user ID session variable, bind the cartName column to the text field. set the OrderID column to use the primary key cartID column and make note of the name that is set in the Store As section.
Next add the eCart Store order Details behavior. Set the Order ID to use the cartdetailCartID column, bind that column to the session variable created by the Store Oder Summary behavior.
Bind each of the additional columns to the corresponding column in the cart object.
You now need to create a page to show a listing of the saved cart. use recordset that queries the cart table and filters the cartUser column on the users ID.
use a repeat region to show the cart name for each record returned. use the cart name as a link to a page that will populate the cart with the corresponding items by passing the cartID as a querystring variable
on the page that will populate the cart, create another recordset that will query the cartdetails table, filter the cart details table using the cartID querystring variable.
on the server behaviors panel, click the plus button and select eCart -> Add to cart -> Get Contents from recordset to use the recordset to repopulate the cart.