Whenever I go where there will be crowds I carry my purse across my chest as I need to carry meds. But for someone who doesn't need to carry a purse and only wants something small I made a Quiltsmart cell phone case for a family member. This will hold a cell phone and credit cards, id and cash. With a long thin strap it can safely be carried almost anyway you want - across your chest, tucked inside your top or even around your waist and tucked into pants pockets. If you are concerned about the card readers just stick some aluminum foil in it to wrap around your card. Another thing I have done is gotten a low limit card and made sure it was 100% protected from liability if lost or account number stolen.
You can't be too careful anywhere and I believe in better safe than sorry. Also the cell phone case will hold my digital camera perfectly and makes an easy way to carry it.
Longarm