Turned off all unused units like the analog comparator, Timer0, USI, and USART.
Saved about 0.2mA. Not much, but I guess worth the tiny amount of effort.
ACSR |= ACD; // Turn off analog compare unit. We don't use it, so save power. Saves about 0.1ma 3.6mA drops to 3.5 mA PRR = PRTIM0 | PRUSI | PRUSART; // Turn off Timer/Counter0, USI, USART since we don't need them. Saves about 0.1mA.
Brownout detector already off via fuses. Won’t really worry about setting IO pins to output since the input is disabled during sleep and we will be asleep almost all the time except when updating display.
I guess it is now all about maximizing time in SLEEP!