The Deleted Scene. It's something that gets cut from a manuscript, a film, etc. because it is deemed irrelevant to the story told. In the last decade or so, it's become fashionable for filmmakers to include some or all deleted scenes as premium content to entice people to buy physical copies of that film. It's also something that you can use for your benefit.
That's why you have a landing page of some sort, right? A blog, a page, whatever- someplace for people to find you, and from which they can go buy your stuff after you sold them first on yourself as a storytelling. Take that stuff you cut from your manuscript and post it there. Use it to sell the book. Take other things you come up with, but won't do anything with for a while, and post them there; A/B test those to see what hits and what misses, and build upon the hits.
Sounds like business? Like selling? It is, and that's because you need to sell to make this more than a hobby. This is particularly important if you're already known for one sort of book and want to branch out to another sort, something writers of series in genre fiction know too well. Since you're going to spend so much time putting together the best manuscript that you think you can make into a viable commercial product, make use of all that you cut away from the final product to help sell it- that's "redeeming the time", the time you spent writing.