The ending of the novel is surprisingly hopeful. After 200-odd pages of gore and wandering, and after The Man dies, leaving The Boy all alone, some kind souls take in The Boy. Throughout the whole book The Man and The Boy have been on the lookout for the "good guys" but they never seem to find them. That is, until the last few pages, when The Boy finds them.
We're unsure what to make of this sudden shift in luck for The Boy. Did McCarthy cave in to commercial pressures and tack on a happy ending? (But then again, we wonder if words like "commercial pressures" even exist for a recluse like McCarthy.) On the other hand, one could just as easily read the ending as a testament to hope and humanity (and all that other good stuff). Meaning, even in the bleakest of worlds, communities (and families) figure out how to keep going. Read this way, the ending possibly suggests that society will rebuild itself.
A not-so-brief side note: Don't forget that The Man's death at the end functions as a type of sacrifice – he's pushed himself hard in order to get The Boy to a warm climate for winter. Then The Boy covers his father with a blanket. In the novel, blankets and food are really valuable items and so this, too, has a touch of sacrifice to it. Anyway, all the talk about "society building" in the previous paragraph really has its roots in the quasi-religious sacrifices The Man and The Boy make for each other. If we had to translate this into Hollywood-speak, we would say something like: [On the red carpet before the Oscars] "This is a novel about individuals doing the right thing despite the circumstances."
You're also probably wondering about the trout in the last paragraph of the novel. We think the description of the trout helps emphasize the beauty of memory despite loss. It also puts into relief all the lyrical descriptions throughout the book. By placing such a pretty description in the last paragraph, McCarthy adds a little importance (we picture paragraphs with puffed-out chests) to all the lyrical descriptions that pepper the text. Just imagine if McCarthy had ended the book with another gory image; the novel would seem less humane. It'd end on a note of warning and despair. Thankfully, this is not the case. We get some lovely trout instead.