NEVER keep your wallet in your back pocket. There are sly pick-pockets lurking on trains all over the city. To avoid getting jacked, move the wallet to your front pocket or a zippered interior slot in your bag or backpack. Also, a tip for anybody head-deep into their smartphones: Don't stand near the door while openly jamming to your music or intensely reading something. The more gutsy theives have been known to grab electronics and purses right out of people's hands, as the doors are closing.