We highly recommend using Purchase Orders to keep a tight control over business expenditure.
Once a PO is in the system you have a much clearer view of likely future expenditure and will have fewer "surprises" when large invoices appear needing urgent payment.
Being able to review all outstanding PO's by Supplier, by GL account and by Job will also help to simplify your month end accounting.
Either chase the suppliers to get invoices to enter into payables (and claim the gst) or decide if you need to raise any month end accruals.
Run the Favourite report Purchases by Status by GL account. This Favourite is looking at All purchases not just those still On Order, so including Paid (Closed) and those still in AP (Open).
Filter to Focus only on PO's in the Order Status
Change the Group by to Supplier to see all outstanding PO's by Supplier.
To see PO's by Job run the favourite Purchases by Status by Job - Detail
Remember to Save any changes you made and create your own new Favourite report that you can run each month end.