I have observed that every purchase you want to make requires a purchase order and then invoice and all that process. There are also tome where little things are bought from non registered vendors and this may not require all those processes as captured in the Erpnext.
I suggest that a “requisition form” be embedded as a doctype where staffers can raise for purchase of little items like Tissue papers, single audio cable for a quick seminar that requires audio facility, and the likes that falls in in such categories.
The Requisition form should have fields like serial num, item name, description, purpose, Amount.
It should be in table form where rows can be added for more items if its more than one item.
At the end of the form, it should have name of person who raised it, dept, and an approver.
Inorder not to make a mess of the major item table where structured purchases and sakes are picked from, a separate item buffer be created which may be called “Requisition Item” where requisition items are created as the items are captured on the form.