What you describe is both a many to many relationship. A contact can be linked to many different items and an item can be linked to more than one contact.
You'd be best served by a join table linking items to contacts like this:
Items::__pkItemID = Item_Contact::_fkItemID
Conteacts::__pkContactID = Item_Contact::_fkContactID
With this set up, you can place a portal to Item_Contacts on the Items layout and you can include fields from Contacts in the portal row to provide details (such as their names) about each contact linked to that product.
Here's a demo file that links contacts to events in this manner: https://www.dropbox.com/s/oyir7cs0yxmbn6i/ManyToManywDemoWExtras.fp7
What I have described here is called the "basic setup" in the demo file.