during the checkout how to grab a list of products at the screen action level?

[Patrick]

Depending on the products ordered, I am changing the flow of the
shopping cart.  I need to grab a list of ordered products at the
screen action level either from the parameters or from a db query.
I've found the item
"shoppingcart=org.ofbiz.order.shoppingcart.webshoppingc...@721c650d"
in the parameters context, so I think I should be able to manipulate
it to give me a list of productIds.   Can you give me a few hints?
Thanks in advance.  Patrick