Perhaps he meets the future versions of his friends. They could show him how they have changed and what they have accomplished. He might also meet new ninjas that he has not met in the present, who are part of the future of the ninja world.
Naruto might meet his future children. He would be able to see what kind of people they are and what their dreams and aspirations are. It would be an emotional moment for him, seeing his family in the future.
Obviously Naruto himself is the most important as he's the one seeing the future. Sasuke would likely be there too, as he's Naruto's closest friend and rival. Sakura would probably also play a role, maybe as a skilled medical ninja in the future Naruto sees. Kakashi might also show up, perhaps as an elder guiding Naruto in his leadership role.
There's a chance he could meet an older and wiser Kakashi. Kakashi might have new insights and stories to share with Naruto from all the years that have passed. And also, he could run into future shinobi who look up to him as a legend from the past.
Maybe Naruto sees himself as Hokage, with the village prosperous and peaceful. He could see his friends by his side, all having achieved their dreams too.
It could be a new character, perhaps someone from a far - off land who has a grudge against Naruto's future self for some reason. This character might be extremely powerful and has plans to destroy everything Naruto holds dear. When Naruto sees this future, he has to find a way to stop this new threat before it even begins to form.
Naruto is the central character, no doubt. Hinata could be important as well. If Naruto sees a future related to his family or his relationship with Hinata, she will play a significant role. Additionally, the Hokage, like Tsunade or whoever is in charge at that time, would be important as Naruto may need to report the future he saw to the village leadership to take collective action.
He might meet the leader of Amegakure. Naruto could also come across some skilled shinobi who are masters of rain - based jutsu.
Perhaps Naruto will encounter some ancient spirits or deities that are native to the island. These entities could have their own agendas and might either help or hinder Naruto depending on how he interacts with them. Another possibility is that he meets some hermits who have been living on the island for a long time and have unique skills or knowledge that Naruto can learn from.
In the 'Naruto goes to the North' fanfic, he may come across a group of nomadic ninjas. These ninjas have a different way of life compared to the ones in Konoha. They might be more in tune with nature and have unique abilities related to the natural elements of the North. Naruto could learn a great deal from them and they could also be potential allies in his adventures in the North.
Naruto might encounter future versions of the kages from different villages. These kages could have different leadership styles influenced by the development of the future world. He may also run into new characters who have emerged as heroes or villains in this new era.
He might meet other wandering ninjas who are also on a quest for power or knowledge. They could either become his allies or foes depending on their motives.