Not hard at all. You can get free OS's which you just install on the usb, or you can go ahead and build your own. I would not suggest attempting to build your own, unless you know what to do, how to do it, and why it needs to be done that way etc. As for carrying a usb, I do purely because I hate hosting my files online. Yes, its easy and I can access from anywhere, but most of the time I work away from a internet source.