Bryon is a young man trying to find his way in the world. He likes being a kid, likes having fun and getting into adventures, but as he gets older he starts to understand the consequences of his actions. As he does so, he becomes morally responsible, although his guilt over hurting people he loves leaves him emotionally wrecked. Here are some symbols from the story that sum up Bryon.
Charlie's car -- The police give Charlie's car to Bryon and Mark. It is a symbol of responsibility because it is a grown-up object and because it was Charlie's, the man who was most like a father figure to Bryon.
Broken Bottle -- This symbolizes Bryon's desire for adventure. He likes fights because of the adrenaline, and even when he starts to question the reasons for fighting, he still admits that he enjoys the fight itself.
Pool Cue -- This is also Bryon's desire for fun and adventure, as well as for friendship. He and Mark spent a lot of time at the pool hall, hustling people for money. It is that action, however, that causes Charlie's death and leads to Bryon's coming of age.
M&M's Peace Symbol -- Bryon like M&M, even if he is a "little weird". The peace symbol is symbolic of the peace that Bryon wants to have in his world. He can't accept that his need to do the right thing has led to a rift between him and Mark - up to the very end, he keeps seeking Mark out in hopes that Mark will forgive him.
Also, M&M's M&Ms represent himself and his youth. A grown adult would probobly not carry around a lot of M&Ms. The candy leads to his nickname.