hi, leaving the lights on auto will not drain the battery. As I believe that is run off power from ignition/canbus. obviously the canbus will keep the lights on for 10-20 seconds whaterver it is for the follow me home feature. once that's cut... no power will be going to the lights. so I would probably rule the auto lights out.
maybe look into the stereo drain issue to 100% rule that out. and your parrot. just disconnect that and see how it goes. If you can be bothered, disconnect both the stereo and the parrot, either the same time or separately and see if the battery does/doesn't drain, it will point you in a direction one way or another.