You can set the security for the entire group to not display, or delete registration items that have not been purchased by a customer. The registration item cannot be hidden unless all of the items in that group can be hidden.

To do this, navigate to:
  1. onMessage > Approval > Event Registration 
  2. Click Edit next to the name of the Event Registration you are trying to hide Items from
  3. Click Registration Items on the left
  4. Click Edit Group for each Item you wish to hide
  5. Unmark the Roles that have access to see those "Group Items"
  6. Click Save or Save & Exit
  7. Repeat this process for each Group.