When creating an invoice, you may wish to include the non-billable items in the same section as the billable ones.
To do this, walk through the regular steps of setting up an invoice. Continue through the first two steps of the Ready To Bill process. At the last step -- before turning it into a full Draft invoice -- click the "Configure Formatting" dropdown.
Enabling "Combine billable and non billable" will group the desired items under the same sub-header.
Save the changes this, or all Clients, and complete the Draft invoice.