The woods, garden and seeds are representative of growth, change and opportunity. When Willy confronts any of these things in the play, Death of a Salesman, it is with a vision that these things will bring a positive change and, ultimately, success--even though, in reality, they are present in the face of certain failure. For example, on the night he dies, Willy is out trying to plant seeds, even though Linda has reminded him that the new apartment buildings surrounding their home block the light. Still he tries, and Linda never discourages him from doing so.
The jungle and diamonds are symbolic of lost opportunities. These are items Willy associates continually with his successful brother, Ben, who (according to Willy) encouraged Willy as a young man to go to the jungles of Africa to make his fortune (in diamonds) as Ben had done. The jungle could singularly be representative of taking risks and going out into the world instead of staying close to home, as Willy did by taking a sales job that brought him home most nights. This is a major source of self-doubt and suffering that Willy continually struggles against.
The diamond is symbolic of the rewards of taking those risks.
The car and refrigerator are symbolic of life's obstacles. These two items in Willy's life cause him enormous frustration. They break down constantly, and Willy feels as if he can never get ahead financially because these expensive, necessary parts of his life are sucking up their resources.
The silk stockings and Linda's washing are symbolic of Willy's inner conflicts. Although it would seem he loves his wife on some level, he is forever speaking over her, telling her to be quiet or emotionally pushing her away. This may be because she is part of his unsuccessful life and he has to face his inadequacies when he looks at her, even though she seems not to notice or hold him accountable for these inadequacies. The washing is part of her life in his home: the everyday challenges of a wife who has never received the things she deserves, and part of him realizes this and he blames himself, though it would seem he does so unconsciously, but still takes it out on her.
The silk stockings are symbolic of his adulterous behavior. It is unclear whether there is only one woman (in Boston, where Biff caught him with a woman) or "one in every town." For the woman (or women) he visits, Willy provides a gift of silk stockings. They are highly valuable to these women, and expensive to buy. For these women, Willy is successful and funny, and they make him feel good about himself. It may be that he is naturally well liked, but it may also be simply because he gives them expensive gifts. He does not give these to his wife, but when he sees her mending her own stockings, he feels guilty and yells at her, telling her to put them away, or to buy new ones.
The symbols listed all represent the overall structure of the play's plot, related in some way to the many conflicts, internal and external, which Willy faces in the play.