My goal: Add some fields to the form uc_cart_checkout_form so that later, when reviewing and processing orders, I have more information than the existing form provides.
I'd like to do this without hacking the core modules because that would break my upgrade path.
I can use hook_form_alter() to add the form fields pretty easily.
I can roll my own submit function into the chain so that I can grab those fields out of the form and store them.
The problem is, I need the order_id.
Now, in hook_order() I can easily get that order information out of the order object. No problem there.
That gives me access to the order_id.
The issue is, I don't know to blend the two.
When I have the order_id, I don't have the form values.
When I have the form_values I don't have the order_id.
Help? 
