Write personal side stories and/or snippets for their characters... Like, I have so many self-indulgent docs. For instance, in my current ongoing book, one of my characters is in a very tragic situation, locked in a dirty cell by the antagonist, and her love interest has taken a job inside of the antagonist's palace so that he can see her and make sure she survives. Like, providing her with proper meals that other of the imprisoned people are not getting or talking with her to maintain her sanity. He cannot do anything to get her out without risking himself. If he dies trying to help her get out, she'll then die without his help. I love them so much... my heart breaks for them even though I'm the one who created them. So, I created a self-indulgent of a few pages where he manages to save her and get her out, but it's not canon to the original story. I'm sure there are many other authors out there who write alternative choices they had, especially if they were torn between two or more different outcomes.
Hiding mistakes like:
Author: "I'm going to create my fantasy institution that is based of this real-world organisation!"
Reader: "Hey, your institution wouldn't work like this. In real life it would do X but you've done Y."
Author: "...That's the real-world one. Mine is different so it can do Y."
I do this so muchhhh. Default all my "modern" worlds are basically very similar to real life but I just change things I hateee, like how the authorities behave and the government system