'A thing of' is a very Irish way of describing an inanimate object, usually a container or packaging of sorts. Be it down to laziness, or actually not knowing the name of what the object is, this expression has many uses.
A bag of chips (thick cut potato fries) that contains and arbitrary number of chips more than a regular bag of chips. The amount of extra chips is at the discretion and generally based on the mood of the person serving as there is no standard measure for a large chip.