Sometimes I will be playing in survival, and I will think of something that I would want to do in the future. So I think that it would be cool if you could somehow craft a pencil out of sticks and coal(or charcoal) and write on paper. It would be like a sign that you could keep in your inventory without the text going away, so you could reference it whenever you needed to. You could make to-do lists, or you could use it to memorize needed cooridinates or anything like that. Sorry if this was already suggested, but I tried to look and didn't see it.
I like this idea, it really has a lot to go off. There could even be the addition of glass bottles. You could put a note inside a bottle, and put it into the water, where it will float off. When it hit's ground, it stays thee till someone finds it breaks it and collects the note. Could be a lot of fun, actually. But, because I should say it anyways, this has been suggested a lot of times. Please use the search bar before making suggestions. I know you said you looked, but I'm surprised you didn't see anything like it. To list off my head, there's a mod kind of already like this that uses books to write in. A lot of stuff is really already made, sorry.
Zombiecraft Maps!