It is with great joy that I clarify this answer...
At @L.Dutch's suggestion, I posted a question about my original answer (below) at Law.SE. That answer is well informed and very much worth reading by anyone who uses Worldbuilding.SE with the worry that they may be restricted in any way by using ideas found via this Stack.
In a nutshell: you have no problems. People who post answers are posting them gratis and your use of those answers to guide your writing efforts leave you in full control of your copyright without dependence.
I'm leaving my original answer in place because, regrettably, I suspect the perception of the limitation will continue basically forever.
Further, the author of the Law answer posted a question and answer concerning co-authorship and derivative works that will also be valuable to the practitioners of the arcane art of Worldbuilding.
This site has one overriding limitation that would minimize, if not eliminate, the cultural objects you seek
Now, I'm going to jump to the conclusion that when you say "cultural object" you're referring to something that either has a cultural impact or was culturally durable — not just something posted somewhere on the web where the public could find it if they were led to it (aka, the digital-age version of spreading a lithographed copy of a short story among friends). So, given that Wikipedia could be considered a "cultural object" (in which case the mere presence of Worldbuilding.SE trivially answers your question), I conclude that such an object must, of necessity, be commercial. Thus the goal is limited if not prohibited by...
The CC-BY-SA license
Proponents of the license will urgently remind you that nothing about that license stops you from using what you learn from here commercially.
It's that second bullet that's the real kicker. How do you get movie rights to your book when your book has CC-BY-SA content, meaning the filmakers can make the movie not only without your consent (so long as you're attributed), but without your compensation.1
To make a long story short, while I wouldn't be surprised to find a commercial use (aka "cultural object") of this site's material out there someplace, I'd be shocked if it was much of a commercial success or that there were very many of them. Because there's no way to protect the copyright (if it exists at all).
I could be wrong about all this. I'm not an attorney. But I have been a publisher and know a bit about copyright. So anyone who disagrees with me should be prepared to show me legal precedent that someone can copy-protect something originally published under the CC-BY-SA license.
Have you answered my question?
Verbosely, yes. There aren't any that I'm familiar with.
1 I'm being intentionally obtuse about this. While the film makers wouldn't need your permission nor be required to compensate you for the CC-BY-SA content in your hypothetical book — it's unlikely that your entire book is CC-BY-SA. It's the same problem encountered by people who write historical fiction. They have no claim over the history, but they do claim their story within the context of that history. So it's not as bad as it sounds... but I'm trying to make a point.