Imagery...

Water, cleaning and washing
Throughout the story, the idea of water and what it can do changes. When it's first metioned, the sentence reads "Deep stone flues where the water dripped and sang" which is altogether a rather beautiful sentence, which creates the image of something created by natures, that's bother tranquil and extradionary.
In the story water is seen as one of the most important things, and takes on the primary purpose of being the most important thing they need to survive and centering their lives.

The mountain
The man and boy travel through the mountains in hope finding something better on the other side. This happens a lot within many books, people travel through mountains, suffering many'a hardship on their way through in the hope that it'll be worth it on the other side, they'll be able to lead a better, saffer life. In this story, the man and boy travel through the mountains, firstly because they're following the path of the birds and hoping to find something better, and secondly because if they stay on the side of the mountains they are on for any longer, they will freeze to death.
Fire
Fire is something that's been with man since the dawn of time, it's one of the main things which originally seperated us from the animals. It's used for survial in the way that it's used for both food and warmth, it's one of mans most basic essentials. Within the story we are brought back to the begining of civilisation when once again mankind is left to rely upon this basic tool, it signals both the regression of society and the fall of mankind.

Sight/sightlessness
In the story, the mans wife is blind. The world is also blind in the sense that it's a dead world. To survive in a dead world, in which hummanity has descended into nothing more than  plagues of savages, roaming around with the aim to hunt and kill, one would have thought you'd need sight, the man's wife proves you do not. I'm unsure whether this is because of the man's help or not, as she manages to leave and kill herself without him. Another thing which makes me believe sight may not be as important as I'd think is the fact that in the dark, when they cannot see they still manage to escape from the bad guys :/

Seeds
Music/musical instruments
Religious imagery
The Coca Cola can

The sea
Through part of the story, the man and boys goal is to reach the sea, a place where they hope things'll be better or adleast appear more hopeful than the dreary and althogher dead landscape they travel across. The first description of the sea we get it "the ocean vast and cole shifting heavily like a slowly heaving vat of slag and then the gray squall line of ash" the whole description being like one long list of negativity. The ocean is not described as one would expect an American ocean to be, as a beautiful blue expanse surrounded by golden sandy beaches, it's instead one that creates a desparingly sad image.

The colour grey (gray American spelling) Ash
Firstly the spelling itself helps to create a sense of place, as it's the American spelling, which is also another huge clue towards the fact that the book is set in America.
Everything from the landscape to the sea is covered in ash within the book. Ash is associated with fire, and ruin, and death, within the story it is also associated with this. Throughout the story, the ash plagues the man and boy, acting as a constant reminder to the loss of hummanity, covering everything that once meant something to someone.