In My Side of the Mountain, Sam awakens Bando essentially because Sam is lonely. Sam has not, at that point, had any human company for a long time. Because he is lonely, he wakes Bando up even though he is afraid that Bando is an outlaw. We can see this in the passage when Sam first meets Bando, before he has “named” Bando.
In that scene, Sam has recently heard police sirens. He now finds this man asleep and he puts two and two together and decides that the police were after that man. He is worried that the man is a criminal and he wonders if he will have to go and hide until the man leaves. But he cannot stand to do that. He does not exactly say this in so many words, but he is lonely. Sam says
How I wanted to hear his voice, to tell him about The Baron and Jessie C. James, to say words out loud.
Sam also says that he worries that the man might be hungry, but it seems clear that his real motive is that he is lonely. Sam has not spoken to another person in a very long time. He has not been able to tell anyone about the animal friends he has made. He is lonely for human company. This is why he decides to awaken Bando.