Cross Platform Encrypted Data Storage on USB Key



I was wondering if anyone can tell me if a program exists or some kind of viable solution is available to meet the following specs.

I need a program that resides and is self running on a USB key that works on both Windows and Mac OSx that will allow me to store text data which is encrypted.

Basically I have private information that I need to carry around with me on a USB Key that I need to be able to access on any Mac or PC. It will only be text, no images etc. I don't want it to leave any kind of trace on the computer it's used on.

Can anyone suggest any solution?

Many Thanks