Sam Gribley is a very independent young man (boy?). He has to be in order to survive on his own in the mountains with little to no help from anybody. Simply to even consider doing it shows Sam's independence, but his follow through proves his independence. The follow through also shows another characteristic of Sam. That would be determination. Some might call it stubbornness, but I am going to go with determination. There just is no quit in that kid.
Despite Sam being fiercely independent, he is not unfriendly. He meets people while on his "journey," and Sam doesn't chase them away like a crazy person. Quite the opposite actually. Bando lives with Sam for a total of 10 days and even comes back to visit later. That tells me that Sam is quite cordial and friendly. Sam is also a creative thinker. It's how he manages to survive with minimal tools for so long. Sam is also humble enough to ask for help as needed. This is indicated right away when Sam asks Miss Turner to help him locate the old farmstead.