Misc. Items are Items that do not exist in your SIX Catalog. You create them on a per Project basis if you want to add untaxed Items to a Project. These are generally used for shipping charges or travel time.
These display on Proposal reports after the Project Subtotal section, and also appear as one line item in the Project Summary of a Proposal. No tax is applied to Misc. Items.
Change your View to display the Misc. Items:
Select the Misc. Item and use the commands on the ribbon to Edit/Delete, or right-click to get options: