Multi-Boot USB Stick

I have created a bootable thumb drive from an ISO using a product from freeisotousb.com My next step is to figure out how to make it multi-bootable so that I can select from a menu and choose what to do.

Potential Uses:
1. It is current only in single-boot mode and is to used to install Windows.
2. I want to make it into a tech drive to contain a couple of live copies of Linux as well as OS installations.
3. It would also be nice to have a data folder on it as well, and some portable apps.  Assistance is greatly appreciated.

I want to keep it simple so if I can do this with a batch file and even without the use of freeisotousb, I would like to.