I've lost it again. Got a new install and can't find it..  even with the afore mentioned module in place. Somewhat miffed I can assure you!

What I've discovered is that you can associate a catalog item to a service offering by adding it to the "Items orderable by subscribers" related list on the Service Offering.  Then, when that item is ordered from the catalog, both the service and service offering reference fields on the RITM are populated accordingly!

Hello Brian,
Could you please let me know, is this functionality of populating both the service and service offering reference fields on the RITM is OOB (part of ITSM plugin) or it requires Service Portfolio Management plugin?

This also allows you to see the catalog items associated with an offering, in DPM. Without doing this they don't appear. For those playing with DPM.   

I don't believe this is true, there can be multiple SO mapped to one catalog item and then the RITM Service/SO cannot be populated correctly.

If it works like that for you, it must have been some customization/