All of these objects are symbols of the fact that there is more to the story than there seems to be.  They are not just trifles.

The unbroken fruit jar symbolizes Mrs. Wright’s secret.  Mrs. Peters is aware of this, because she goes looking for this.  When the men first find the fruit jars, they are annoyed.  They are annoyed and confused by the kitchen in general.  This is where the title of the play comes from, when Hale says women worry about “trifles.”   

She worried about that when it turned so cold. She said the fire'd go out and her jars would break.

He’s frustrated by all the broken fruit.  But Mrs. Peters knows to keep looking, and she realizes that Mrs. Wright worked hard to can that fruit, and she looks for Mrs. Wright’s secret.  She finds it.  The men are clueless in the kitchen, but the woman knows where to look.  She realizes there is more to see here, and there is more to this story.

The canary is also important because it symbolizes Mrs. Wright’s maternal instinct.  It is understood that Mr. Wright killed the canary, which she keeps hidden in a box.  When the women find the bird, they are unable to touch it.  It is as if they understand the magnitude of what he has done, but continue to town the line.

My, it’s a good thing the men couldn’t hear us. Wouldn’t they just laugh! Getting all stirred up over a little thing like a—dead canary. As if that could have anything to do with—with—wouldn’t they laugh!

Mr. Wright was continuously crushing her soul, like he crushed that little bird.  They can talk about the law punishing her all they want, but what about him?  He is unreachable, because he is dead.  He was clearly some kind of monster too.  When asked about the bird, they tell the sheriff they think cat got it.

The quilt is a symbol of the household, and this one is hidden away, unfinished.  It is with the bird.  Mrs. Wright does not have a happy home.  She has a home of shame, misery, and isolation.  Her life is empty and sad.  The fact that the ladies wonder if she was going to knot the quilt is funny to the men, who don’t think it’s important, or who think it’s morbidly ironic given the strangulation of her husband, also shows how lonely she was.  Where were these ladies while Mrs. Wright was alive?  Where was this conversation then?  Mrs. Hale realizes this.

Oh, I wish I’d come over here once in a while! That was a crime! That was a crime! Who’s going to punish that?

The rocker represents the isolation and loneliness that Mrs. Wright felt.  When she was found, she was just sitting in the rocking chair, pleating her apron, rocking back and forth.  She lived with that man, and she never had any visitors, and she was alone.  The isolation got to her, and she could not take it any more.  Sometimes the little things in life are the ones that matter.