There's also a chance that an old enemy who has had a change of heart, like Gaara (even though he's now an ally but for the sake of the fanfiction), might visit Naruto in the cave. He could offer his help or just come to talk and share their experiences of being outcasts in the past.
Maybe some of the younger ninja like Boruto or Sarada could stumble upon Naruto's cave while on a training mission. They could be curious about this strange hermit - like figure in the cave and later realize it's Naruto. This could lead to a mentoring - like relationship between Naruto and the new generation.
His old mentor, Iruka, might visit. Iruka has always cared about Naruto. He could bring some supplies and words of encouragement. He might also be worried about Naruto's well - being and want to make sure he's okay living in the cave.
Dumbledore might make an appearance. He could come to give Harry some advice or to share some important information about the war against Voldemort. Dumbledore might also be interested in seeing how Harry is faring in the old Black family house and if he's discovered anything of significance there.
Sasuke could visit him. Despite their differences in the past, they have a deep bond. Sasuke might come to check on Naruto, or maybe he also wants some time away from the world and thinks Naruto's seclusion place is a good spot.
Arthur could visit Merlin in the tower. He might be curious about what Merlin does in his secret place or he could be in need of Merlin's help and follows him there.
He might meet other ninjas who have gone rogue or are in hiding for various reasons. These could be ninjas who have had a falling out with their clans or the village leadership.
There could be a rogue ninja hiding in the cave. This ninja might be on the run from the authorities and has some secrets that Naruto is interested in. Maybe they end up teaming up for a while.
The old ninja masters could visit Naruto's shop too. They might be interested in seeing what new and innovative things Naruto is doing with his shop. Some of Naruto's former teachers like Kakashi could also drop by regularly. He might give Naruto some advice on running the business or just come to have a friendly chat while browsing the items in the shop.
His best friends, Ron and Hermione, would most likely visit him. They have always been by his side through thick and thin, so they would find a way to get to the tent to check on him, bring him supplies, and offer their support.
He might meet the samurai of Iron Country. These are warriors with different fighting styles compared to the ninjas. Naruto could learn a great deal from them, like their swordsmanship or their sense of honor.
His friends like Sasuke, Sakura, and Kakashi might visit. They could come to relax and catch up with Naruto.