Commerce Split Checkout

This module provides a framework for "splitting" the checkout into a new order. You can provide an option to the user to "Save cart for later" and proceed with a new order that has a checkout process flagged with a query string ("/checkout/[ORDER]/page?cmode=process_name").

I wouldn't recommend getting into this unless you're ready to read through code comments and are familiar with Drupal hooks.

Split checkout process

1. Link user to checkout-splitting page
2. Provide user options on how to continue
3. Save current order for later
4. Allow user to checkout with new order
5. Reload order that was "saved for later"