I bring in a USB stick (now -- it used to be a CD, and before that a floppy disk) containing programs I've written (both executables and the source) as well as

I bring in a USB stick (now -- it used to be a CD, and before that a floppy disk) containing programs I've written (both executables and the source) as well as example documentation, white papers, etc., when appropriate to the situation. I choose what goes into the portfolio specifically to demonstrate not only how I think as a dev, but also techniques and skills that I think are likely to be relevant.