Ready Player One is a recent book and upcoming movie that makes heavy usage of famous (and less famous) characters from video games (also movies and shows). Did the book have to get permissions and license from the copyright holders of all those creators? Would the upcoming movie have had to get fresh licenses for its usage? This sounds like it would be prohibitively expensive since they use many extremely popular characters.
Did the book have to get permissions and license from the copyright holders of all those creators?
Probably not. This probably wouldn't have counted as a covered derivative work entitled to copyright protection and might have amounted to fair use with just mention in the text of a book
Would the upcoming movie have had to get fresh licenses for its usage?
Yes. It almost certainly did, probably at some considerable expense (although the producers may have already owned the rights to many of them) and there were probably some editorial changes in the characters made as a result of the negotiations to replace expensive licensor demands with less expensive characters.
Also, keep in mind that contracts can be creative and often are in the financing of movies. The license was likely for a percentage of profits rather than a flat dollar amount, which was budgeted to be reasonable. No license means no inclusion in the movie and the loss of exposure if not included is an incentive to deal in addition to the license fee as exposure may increase the value of the licensed property if the movie is good.