One good example is the broken jam jars in the cupboard. Minnie, in jail, worried that the cold would cause the jams to expand and break. The men comment that this is a typical "trifle" for a women to worry about; aside from the culinary pun, the word becomes very important later when the "trifle" of the dead canary comes to light. The jam jars symbolize Minnie's life, and how it has gone from being worthwhile to being empty.
MRS. PETERS: [To the other woman.] Oh, her fruit; it did freeze. [To the LAWYER.] She worried about that when it turned so cold. She said the fire'd go out and her jars would break.
SHERIFF: Well, can you beat the women! Held for murder and worryin' about her preserves.
(Glaspell, Trifles, etext.virginia.edu)
Minnie worried about her preserves because they represented worth in her life. Like the jars, she used to be a vessel for something good, but living with her husband sapped her emotional strength and left her hollow inside. Like the jars, the cold abuse of the house caused her shell to crack, slowly leeching out everything in which she took joy. Finally, she felt forced into a corner, and now there is only her empty shell left; all the jam (happiness) in her life is gone.