i heard of the eternal stew at a Renn Faire last year, though I'm sure the lady called it something else, can't remember what though.
No rules or specific ingredients; just toss in whatever you've got at hand when it stew starts to get thin. I'd advise always adding ingredients to one side of the pot and serving from the other, to ensure that what you served was cooked. It's a great idea if you're running an inn, but in a survival situation, I think it would be more economical to cook food as it's needed, rather than keeping the pot simmering constantly, as the latter would consume a lot more fuel.