Wow! I just watched this youtube video where the guy demonstrates a set of stick-on buttons that he refers to as “nipples”. Basically you just stick them onto the back of your android phone and launch an app in order to configure which app you want to launch with each button. You can then activate things like the camera and torch at the touch of an external button.
Looks a bit ugly and no clue how they work with no power, but I’m gonna get some!