DIY mini shields
For many projects you only need a few pins and the power lines GND and VCC.
Have a look at the connectors IOL (d0 - d7), IOH (d8 - d13) and Analog (A0 - A5).
Only the IOH contains the GND pin.
And there is also a AREF pin.
Can this pin be used as power supply?
Well, if you do not need the analogRead(), and you only need a few milliamperes you can.