My wish would be that every time I opened a book, I would enter that world as a character at my current real life age. I would then live inside the book until my death. When I died in the book, I would return to my body in the real world at the exact instant I opened the book. I could then reenter the same book at the beginning or at the point of my death, even if the point of my death was after the point the book ended. The story would just continue past the written point just like real life. I could do this with as many books as I wish, in any world I wish. I would be immortal, but with the choice to age and die at any time. If I entered a realm with magic, it would be like I had wished for superpowers as well. I've thought on this before.