I wrote about the following on another website, you do what you want with the info.

sooner or later, it's gonna happen. you go off on an excursion, or just to a beach somewhere, when nature calls. if you're lucky, there's a public facility around, but all too often, they're filthy. no seat ,no paper, you get the idea. well, someone came up with a great idea, ( and it wasn't me ). go to http://www.biffybag.com/ to see what I am referring to.. being in construction, I can appreciate these, and wish I'd had them on several occasions.
sorry, you can't just click on the link
they can also be purchased on Amazon

you're welcome