I think that one way that Max shows courage is in his "rescuing" of Kevin. He does not shy away from helping his friend and even though he is simply following what Kevin says, in the end, the action of rescuing Kevin is what others point to in their praise of Max. This is the most elemental way in which courage is shown in chapter 8.
I would also suggest that courage is shown in how Max does not shy away from Kevin. As Kevin keeps on talking of Arthurian legends and "archetypes," Max does not flinch from this. He does not retreat into an inward shell when it is evident that Max is brighter than him and using terms and concepts he does not get. In short, he has the courage to allow a friendship to exist despite the intellectual differences between them. This shows courage because it shows Max taking a chance and a risk. It is in this light where Max shows courage. He does not let frustration and difference insulate him and cut him off from another human being. Rather, he is able to have the emotional courage to bridge difference and forget friendship with one who is so different than himself.