Significance of the Symbols
This is a quick look at the four primary Death of a Salesman symbols.
Seeds. Willy spends time outside at night planting them, in a harebrained attempt to grow the food that he can't afford for his family, since he's not doing much at all in the way of earning a commission. Planting the seeds is labor that can pay off for him directly, in a way that driving around and having the new representatives of his former customers laughing at him cannot. Seeds represent his feeling of failure as far as leaving a legacy for his children, as well as his failure to raise young men who would turn out to be a success -- particularly in the case of Biff.
Stockings. Willy's always asking Linda what kind of shape her stockings are in. If she has ratty stockings, to him that means that he is a poor provider, because he can't afford to keep her in new ones. Also, when Biff catches Willy in his affair, in the hotel room in Boston, he accuses him of taking his mother's stockings and giving them to his lover. And so stockings also take on a symbol of this unfaithfulness: by giving Linda new stockings, Willy assuages his guilt for the affair.
Diamonds. Willy's brother Ben made unbelievable wealth for himself in the diamond market in Alaska. For Willy, diamonds represent the kind of riches that you can hold in your hand, as opposed to commissions that you have to wait to get when they come in. Willy's final journey comes when he sees his brother Ben again, now a ghost, urging him to come into the "jungle" -- in the play, Willy's trip into the jungle is a suicidal car accident that provides for his family in a way he could not -- with the insurance payoff.
The Rubber Hose. Linda and Biff keep finding this lying around. Willy has been trying to sniff gas out of the furnace in yet another way to end his own life. Willy's family knows this without acknowledging the possibility -- this generation was not the generation of psychoanalysis.