How to minimize a smartphone's battery consumption?

I'm not looking for suggestions that mention carrying power banks or charging strategies, as this is for in times when I won't be able to use them. Don't worry; this is a hypothetical question and I'm not in any problem.

I want to be able to maximize the phone's potential as an offline, portable computer.

What I already know: - Using airplane mode to prevent antennas from drawing power. - Keeping screen off as much as possible. - Removing any and all memory consuming widgets and live wallpapers. - Use a pitch black wallpaper. Useful at least on an OLED display.