One of the coolest things I've ever gotten in a boxed copy of a game was by far ...
The Age of Empires II: The Age of Kings Civilization Attributes fold-out (4-piece cardboard foldout)
It would be cool to get something like this included in the Collector's Edition Box of Project Eternity
it could include
Race and Class information, Stats information, and Skill trees or something like that (just general race and class foldout of some sort)
But yeah just a hint, paper doesn't last like cardboard does.