What are some symbols or metaphors and what are their meanings in the story?
Perhaps the most salient symbol in "The Count of Monte Cristo" by Alexandre Dumas is the little red purse that originally belongs to Edmund Dantes father. This purse originally contained money that was given by Monsieur Morrel to Dantes's poor father after Caderousse extorted everything from the man. After his return to Marseilles, Dantes recovers the purse and later fills it with a gem that will pay a debt which Monsieur Morrel now owes. In essence, however, Dantes has repaid his debt to Morrel. When Morrel recognizes the old purse, he is puzzled how the donor has been in its possession.
Some interesting images are evoked by Dantes himself with his reflection from Chapter IV, "The Betrothal Feast":
Joy has that peculiar effect that at times it oppresses us just as much as grief.
When Danglars asks Dantes if he is anticipating trouble, the young man replies,
I cannot help thinking it is not man's lot to attain happiness so easily. Good fortune is like the palaces of the enchanted isles, the gates of which were guarded by dragons. Happiness could only be obtained by overcoming these dragons, and I, I know not how I have deserved the honour of becoming Mercedes's husband.
similes: He [de Villefort] was astonished at her[Mercedes] beauty and dignity, and when she asked him what had become of him whom she loved he felt as though he were the culprit and she his judge....Embarrassed by the straight look she gave him,...he pushed by her...Like the woounded hero of Virgil he carried the arrow in his wound.