The Winchester rifle Roy gives to Jack serves as a symbol of the power and control Jack so desperately craves. Because he is just a boy, Jack is powerless to protect himself and his mother from violence, poverty, and unhappiness, and it is only when he has the rifle in his hands that Jack feels that he is more of a man than a boy, and has at last acquired some small scrap of authority that might otherwise be impossible to attain. When Dwight takes Jack's rifle to the turkey shoot, he is symbolically revoking and claiming for himself the power that Jack once had.
The dying salmon that Dwight points out to Rosemary and Jack, swimming from their home in salt water to fresh water so that they may spawn, are symbolic and darkly foreboding of the move that Jack and Rosemary will soon make from Seattle to Chinook. Having left their home, the salmon are dying, their bodies being stripped of their pink flesh as they reject their new environment. Like the salmon, parts of Jack and Rosemary will die once they move and are subjected to Dwight's cruelty and pettiness.
The beaver that Dwight kills while driving Jack "home" to Chinook for the first time is symbolic of the future that awaits Jack, who is about to become like the beaver, helpless and at Dwight's mercy. Two years later, Jack finds the beaver in the attic. It had been left in a basin to cure and was soon forgotten about, just as Jack feels he has been forgotten since his arrival in Chinook. Over time, the beaver has decomposed, sprouting two feet of mold that bear an eerie resemblance to its living form. Jack is comparable to this beaver in that he has has become a mere shell of himself while living under Dwight, even though he is physically the same.