Métro & Trains, Paris
When using the train system, always keep your valuable items close to your body and within your sight. Watch out for the prodessional pick pocketers. I did witnessed one pick pocket incident and they worked like a professional.
The Métro tickets are so tiny,you could easily lose them.So put them somewhere safe in your bag if you don't want to be paying for another ticket.
there is a bit of confusion here, since the platforms are at two distinct stations and one of them a few mnutes walk away and not luggage friendly.
Metropolitain: Don't let things without watching even for a second, You lose them quicker than You expect!