He becomes more resourceful. In his own time, he's used to a certain set of circumstances. But during time travel, he has to adapt quickly to new situations and find ways to use the resources available in the past. For example, he might have to figure out how to use different senzu beans or power - up techniques that are new to him.
Cell could still be a great antagonist. Imagine a scenario where in the fanfiction, Cell follows Future Trunks through time. He then starts to absorb different beings in the new timeline in a more devious way than in the original story.
Well, there's a fanfic called 'Trunks' Time - Travel Tales' that's really good. It plays around with the concept of Trunks' time - traveling in a very creative way. Then there's 'Future Trunks' Love Story' which, as the name suggests, focuses on his romantic relationships. Also, 'The Legend of Future Trunks' is a must - read as it expands on his character and his place in the Dragon Ball universe.
One idea could be Future Trunks bringing back a technology from the future that changes the course of the present timeline's battles. For example, a more advanced scouter that can detect hidden power levels more accurately.
One possible plot could be Future Trunks traveling back in time to prevent a new threat that he discovers in his own time. For example, a powerful and unknown enemy is about to emerge in his future, and he goes back to enlist the help of Goku and the others before it's too late. Another plot could involve Trunks accidentally changing something in the past that has unforeseen consequences in his future, like messing with the timeline of a certain character's power - up, which then leads to a whole new set of challenges when he returns to his own time.
One common theme is time-travel. Since Trunks is known for his time - traveling adventures, many fanfictions explore this aspect further, like dealing with the consequences of changing timelines.
She can be quite independent. In fanfic, female Future Trunks is usually shown as someone who can make her own decisions and follow through with them. She doesn't rely on others easily and is confident in her abilities. She might go on solo missions to save the day, which shows her self - reliance. Moreover, she may also possess a unique sense of style that sets her apart from other characters in the Dragon Ball universe, which adds to her charm in the fanfic world.
Definitely their strong bond. They have been through so much together, so highlighting their loyalty and trust for each other is great. Also, their different fighting styles can add action - packed scenes. For example, Gohan's more methodical and strategic approach against Trunks' more impulsive and aggressive style.