I agree, common sense and intuition are both very useful. Of course you need to check all needed stuff before you left every place, I often missed my bag that later caused problems to others that helped me. I also tend too much often to forgive my phone and this leads me back the way to it.
I assume I must be more in alert on this things to not happen too much frecuently.
Your post reminded me of being aware not only from others but from myself.
I always followed the same rule as you Madlen to try and be invisible or at least if visible be friendly and smile and get away of the front of threatening people. However I sometimes during my youth had to face dangerous individuals and had to show no fear but send the message I would not be an easy target, that worked for me as I'm here to talk to you.
Be invisible or be dangerous, be careful and be brave, use you common sense and don't get too paranoid.
Cheers ;)