Non-Stock items refer to any Item that does not require inventory tracking, usually this means something intangible, such as Charges.
How to Create a Non-Stock Item
You can edit any existing item, or create a new item via the Setup > Items screen.
There is a Non-stock checkbox in the Configuration section.
Best practise is to have a dedicated "Misc" or "Charges" item type for these.
Common use cases
It can be a good idea to setup a generic placeholder item, for one-off cases where you don't necessarily want to create a new item, it can fill in for anything.
Usually, it's best to set them up with a name such as "PLACEHOLDER" which can later be renamed when added to an invoice.
Damage waivers use the Non-stock function, see help doc for more details.
If you need to track your own vehicles or other assets so you can create maintenance records or simply track their usage history on jobs, then you can create them as a Non-Stock item.
It is good practise to assign them to a unique Item-type to keep them separate from your regular items.
Delivery Charges (And others)
Delivery charges, or any other type of charge are best configured as a Non-Stock item.
Best practise is to assign Charges to their own unique item type to keep them separate from regular items.