A father and son travel together across a ravaged earth heading south in the hope of finding some form of humanity, while avoiding murderous bands of cannibals and trying to survive from day to day with the little amount of food they can find.

Not exactly a feel-good movie!  The father's mission and ultimate goal is to protect his son from harm, which means that he has become cold-hearted to others and unwilling to help his fellow man for fear that no one else could truly be trusted.
  They stumble upon an underground bunker with shelves full of tinned rations to help replenish their bodies and help keep them going a while longer, but a dog barking near the sealed cover one night frightens the man enough to make them leave their sanctuary and continue heading towards the coast - their new plan B.

They approach a nice plantation style house with a locked basement near a bundle of old shoes (big clue). Inside the man is attacked by starving and mutilated victims - they get out but shut and block the cellar doors to seal the poor guys inside as 4 cannibals approach their home.
  The man and boy hide and he prepares to kill his son, rather than fight, but some of the prisoners escape giving them a diversion to get away.

Reaching the coast, its not much better and while the man is out swimming someone steals their stash. They catch up with the thief, and the father forces him to strip and takes everything off him, leaving the desperate man to his death against the wishes of his son.

The father (known in the movie only as 'the man') is quickly growing even more paranoid and kills an archer with his flare-gun thinking they were being followed, before he becomes ill and at the coast gives out.

Guy Pearce is a long way from home and approaches the boy. He tells him they've been following the boy for a while and will protect him. Slowly the boy believes him, says goodbye to his dead father, and then joins Guy's family which has a few women, other kids and even a little dog which has survived the nuclear holocaust and done a lot better than all the dead cockroaches.

Fans of the book will hate me for saying this, but honestly I thought "The Book of Eli" was a much more rounded movie. I'm not a fan of this "Mad Max" style apocalyptic future at the best of times as all these movies are basically the same thing without any hope or point to watch it, but The Road really was over-hyped with this "rated 4 stars by critics" advertising in the tv trailers. The sub-plot of the shaky hands in Book of Eli was a nice touch - and did they really need to bring in a lone wanderer in The Road who happened to be called "Eli" with poor eyesight? I know movies are usually released in pairs by rival studios, but that decision was a little strange.