As a writer I have a lot of ideas and a lot of them end up sitting in notebooks or my brain waiting to be included in a story. They become so faint that I won’t make them their own story, but I can use them as inspiration for new ideas which will in turn become their own stories. Most of the time these old ideas are just simple characters and settings which never get used, sometimes they are entire scenes complete with a plot, characters, and an interesting setting.
By using these ideas when you write a story you make sure they don’t go to rest. Also it can become interesting to explain where all the ideas you used in a story came from. Another thing you can do is add a personal Easter egg into your work. I have a few characters whose names I will never forget because they are my first characters. I sometimes use at least the names of these characters in my work if there is a side character who will only show up for a few scenes who needs a name. Other times I will add subtle references that no one will get unless they know the stories of these characters. It can be fun to use old ideas in your work.