Purchase Order With Non-Inventory Items?

I seem to not find a way to add a non-inventory item, like shop supplies or office supplies, to a purchase order. I would also need to select the proper expense category. I found a forum post from 2010 that mentioned there is no problem adding non stock items, but I don't see how to do this. At times, I need a PO with both stock and non stock items on the same order.

  Also, looking for a way to record non-physical purchases like a shipping label where I now enter a misc voucher and the selected vendor directs the record through a outbound freight GL account). I pay off the collection of labels at the end of the month. Is this where I want to use a "Direct Supplier Invoice"

  Thank you!
Paul