I have to say it is a handy place to put it, less likely to lose it.
When I go out/Clubbing, I put my emergancy cash/credit card in my bra incashe I loose my bag. Thankfully I have never had to get it out though!
Great Idea, on the other hand we guys can put some cash and cc for emergency in our underwears. But the question is when we get it out will the people accept/touch it. Coz coming out from bra will be happily accepted maybe also given discount. :D