This is a dumb question, but is it possible to deliberately give up copyright on one's work?
(Like, people can use the characters and situations without crediting you or involving you in any way?)
This is called releasing your work into the public domain. Wikipedia has an excellent article on the subject, especially with how it relates to wikis using the material.
There is also the CC0 license which is a ported public domain license which includes support for countries without the notion of public domain in their copyright law.