The Pirate's stash
After the Pirate turns over his sack of coins to Danny for safekeeping, it becomes representative of the bond between the friends. It is a lot of money in the sack, but it none of the friends take it because their friendship is worth more. The Danny and his friends, the coins cease to exist as currency that they could exchange for wine or food. It becomes simply a part of their daily ritual. When Big Joe forgets his place and takes coins from the bag, the reaction of the friends is so harsh because it is not merely a theft of money; it is an attack on their friendship.
The Black Bird
Whether or not the story is true or not, the fact that Pablo claims to see a supernatural huge black bird hovering over Danny on the dock is very important. The bird represents death. Even in his wild month of crime and sleeping in the forest, Danny realizes that he cannot get away from it, that there is no way to regain his use. On the night of Danny's party, death is very close to him indeed.
The Machine Gun
It is very easy to miss, but the machine gun that Danny and his friends discover on the beach after the sinking of the coast guard cutter is an important symbol. It is an invasion of the town of Monterey by a modern technology, and no one realizes its use or value. Though the gun alone must be worth well over five dollars, Danny includes it with all the other junk that they find for just that amount. It is part of Steinbeck's commentary on the innocence of the paisano that they have no idea of the value of such an object, and no idea or desire for its destructive powers.