I feel that one message of the novel is that hope is truly the only thing that matters. From beginning to end, the father emphasizes that the boy "carry the light," a symbol of decency, kindness and humanity in their barbaric world; that light is hope, and it keeps both father and son going. And despite the fact that the boy sees horrific brutality, lives in a wasteland, and is constantly fighting off hunger and illness, at the end, he still carries that light. That means, that in the boy at least, hope has not been quenched in his heart and perspective. Despite circumstances, hope is still there, even if it is in the tiny form of one flame in one survivor's heart. It is when that hope is quenched that darkness truly reigns.
I disagree that The Road is a hopeful book. Nothing is growing in the landscape except morel mushrooms. Nothing (aside from the mushrooms) is edible except foods that were canned before the nuclear war and the bodies of the few people who still live. In an environment so severely damaged, the human race will die out.
The subtext of the novel strongly suggests that the characters know the human race is going to die out. Note how the boy constantly asks how long man-made features like bridges will last. I believe he is really asking how long those objects will outlast humanity.
It's wonderful that the boy finds kind people who will take care of him while he survives. But he will die, probably childless, and so will everyone else.
I tend to think that everyone always gets the idea that things were better back in the day, whatever day that day was. And we will always do that, but it is hard to argue with the idea that things were better before the clouds of ash and nuclear holocaust that we assume started things going in The Road.
Yet people still manage to find ways to carry on, still manage to find the motivation to do what they think is right even when everything looks incredibly bleak and hopeless. So I think in the portrayal of the triumph of human goodness over so much terror and sadness and despair is where it offers hope.
There is also a hopeful ending, where the Father has died, but the son is rescued by what is basically a good Samaritan--someone else who has retained both his humanity and sanity--and leads him back to a colony of others who are trying to start society once again. There is also the hope of reaching the ocean, which is their short term goal. Even though they don't specify how this would be an improvement in their situation, they hope it will be, and that this can lead them farther south towards something better.
I think there is significantly more hope offered in this text than in Oryx and Crake that you also asked about. In this text, hope is offered mainly through the innocence of the son who insists on identifying and affirming the innate goodness in people and argues with his father when his father acts in a way that is cruel. In a sense, the boy is the one reminder of the human conscience - it is he who stops his father and insists they share a meal with the old man they meet and also it is he that insists they give back the clothes and some of the food to the robber who steals from them whilst they are on the beach. In this dog-eat-dog world, it is the boy who represents the last voice reminding humans of their humanity. Thus his survival at the end is very hopeful that this terrible scenario might improve somehow.