So far, the only time I left the key in the Triumph is when I've been working on it. It's really easy when you put the key in to get it out of the hand, check the chain check the oil, start it up and tune the carbs, shut it off, go get the multimeter, start it up and check the alternator, shut it off, check the tire pressure, etc, go wash up and forget the key.
My brand X bike is a totally different story because it has the old style ignition switch. On those, you unlock the switch and drop the key in your pocket. Turn on the switch and go. Then, you turn off the switch, take off the gloves glasses etc. get the stuff out of the saddlebag and try to remember to dig out the key and lock the switch.
