One of the most common characters is definitely her father, Ned Stark. Since Sansa has the chance to go back in time, she would likely interact with him a great deal to try and change the course of events. Another is Arya. They could team up and use their combined knowledge and skills to make a difference. And of course, Littlefinger. Sansa would be more aware of his manipulations this time around and might interact with him in a more strategic way to outwit him.
In this type of fanfiction, a great plotline could be Sansa influencing the political landscape much earlier. She could use her knowledge of how certain houses would act in the future to her advantage. For example, she could form early alliances with houses that she knows will be important later. She might also try to change the way her family views certain people. Maybe she could convince her father to see Littlefinger's true nature much sooner. This would not only protect her family but also change the entire power dynamic in Westeros.
Sansa would be more assertive in her political moves. She has seen the consequences of inaction and bad decisions in the future. So, she would be quicker to make decisions that benefit her family and herself. For example, she might be more involved in military strategies to protect the North.
One idea could be that Sansa goes back in time and tries to prevent the Red Wedding. She could use her knowledge of the future to warn her family and change the course of that tragic event.
Another theme is power. She may use her knowledge of the future to gain power or influence in the past. This could be political power, like influencing the decisions of the lords, or personal power, such as learning combat skills earlier. It's about how she can rewrite her own story with the advantage of hindsight.
She could meet her younger self. This would be an interesting encounter as she could offer advice and guidance to her younger version. Maybe she could help her younger self to be less afraid of her powers.
One great Sansa back in time fanfiction is 'Sansa's Time - Travel Adventure'. It has Sansa going back to key moments in her family's history and trying to change things for the better. The story is really engaging as it shows Sansa using her wits and new - found knowledge from the future.
He could change the course of major events. For example, he might prevent the rise of a powerful villain. This would have a huge impact on the entire galaxy. Maybe he could save some characters who died in the original timeline.
One interesting aspect could be that Luke goes back to a time when the Sith were just emerging. He could try to root out the Sith threat before it became as powerful as it did. He might have to be very careful not to disrupt the timeline too much, but his Jedi wisdom could be a great asset in this time - traveling adventure.
In this fanfiction, Sora might change key events. Maybe he could prevent some of the tragedies that occurred in the original story. For example, he could save a character who was lost before.