Pullup all unused pins to minimize power consumption.

[horsfield2001]

11.2.6 Unconnected Pins
If some pins are unused, it is recommended to ensure that these pins have a defined level. Eventhough most of the digital inputs are disabled in the deep sleep modes as described above, floating inputs should be avoided to reduce current consumption in all other modes where the digitalinputs are enabled (Reset, Active mode and Idle mode).The simplest method to ensure a defined level of an unused pin, is to enable the internal pull-up.In this case, the pull-up will be disabled during reset. If low power consumption during reset isimportant, it is recommended to use an external pull-up or pull-down. Connecting unused pinsdirectly to VCC or GND is not recommended, since this may cause excessive currents if the pin isaccidentally configured as an output

[sobrinho]

@rocketscream ping