There are so many possibilities. He could explore a hidden cave in the forest where there are strange markings on the walls. These markings could be a map to a powerful ninja weapon. Naruto might also have to deal with a forest spirit that is angry because humans have been polluting the forest. So, he has to find a way to make peace with the spirit while living in the forest.
In the fanfiction, Naruto could have adventures like finding a secret waterfall in the forest that has special chakra - enhancing properties. He might have to fight off bandits who are trying to take over the forest for their own evil purposes. And he could also meet a hermit who teaches him some new jutsu that are specific to the forest environment.
He might have battles with strange creatures. In fanfiction, the Forest of Death is full of unknown threats. Naruto could discover new jutsus while trying to survive there.
Well, he might encounter rare and dangerous beasts. Maybe he discovers a hidden power source or an ancient artifact. He could also meet some reclusive and powerful shinobi who have made the forest their home.
He might have adventures like befriending forest animals. Maybe he discovers a hidden magical spring in the forest that has special powers.
Naruto adapts by becoming one with the forest. He observes the animals and learns from their behavior. For example, he sees how squirrels store nuts for the winter and starts doing something similar with his food supplies. He also gets used to the sounds of the forest at night, which at first might have been scary but then becomes a normal part of his life. He may even start using the natural elements of the forest like vines to help him in his ninja training.
Well, he might encounter unique creatures. Maybe he'll befriend a magical deer that helps him find rare herbs for his ninja training. He could also build a really cool tree - house as his hideout, and use natural elements like vines and branches to set up traps for any potential enemies.
She could have encounters with magical creatures that are rarely seen outside the forest. For example, she might come across a group of centaurs and have to earn their trust through her intelligence and respect for their ways.
She might have encounters with wild animals and learn how to survive. Maybe she discovers hidden treasures or makes friends with forest spirits.
He could encounter rogue ninjas. They are always lurking in dangerous places like the Forest of Death, looking for easy prey or valuable items.
They could face a new and powerful enemy that wasn't in the original story. Maybe a strange beast that has the ability to manipulate shadows in the dark forest. Naruto would be all fired up to fight, while Sakura would be using her intelligence to figure out its weaknesses.
The doll girl might face challenges like finding food and shelter, or maybe encountering wild animals.