There is another system on Cessna 172's not mentioned yet, and that is the Fuel Cut Off Valve. Yesterday I flew a Cessna 172R (2000 model with steam gauges) this had a Fuel Selector for "Left", "Both" and "Right". The traditional "Off" position was not available.
The Pre-start Checklist called for the Fuel Cut Off Valve to be closed (pushed in), and the post shutdown checks called for it to be opened (it comes out about 3"). The valve is located just above and to the right of the Fuel Selector switch.
It is not shown on the diagram posted above.