I didn't carry with me a specific amount of cash. Let's say I have normally 20-50 euros (30-70USD more or less) whit me. Sometimes no euros at all.
Anyway, I have always with me a silver dollar (date: 1924, a Peace Dollar http://www.silver-coins.org/1924_peace_dollar.html). My grandad gave me when I was a child: it's my amulet since :-)