This is good question. It really depends on what your paper is about. Let me say a few words on conclusions and then give you some suggestions.
First, a conclusion should not introduce something new. A conclusion needs to bring resolution to your paper. In other words, it brings together your thesis and your supporting points. It shows the reader that your paper is cogent and has stayed on target.
In light of this, your conclusion should recap your points on symbolism. Even if the works that you are working on are not related in theme, they are related in that there is the use of symbolism. Your point can be that all works use symbolism in different ways. Or your point can be that symbolisms are used to create different effects. Or your point can simply be that there are variety of symbolisms.
When I wrote to ask you about your question, you mentioned a number of different stories. Four with which I'm pretty familiar are Flannery O'Connor's "A Good Man Is Hard to Find," Ernest Hemingway's "Hills Like White Elephants," Charlotte Perkins Gilman's "The Yellow Wallpaper," and Kate Chopin's "The Story of an Hour."
As it happens, imagery of nature is used strikingly in all these stories, so perhaps that could be your focus. In O'Connor's story the woods near the end symbolize death; in Hemingway's story the contrasting landscapes symbolize life and death; in Gilman's story the outside and gardens symbolize freedom and life; in Chopin's "The Story of an Hour" the view out the window symbolizes life.
So perhaps you could discuss the use of nature symbolism in these stories to suggest life, vitality, happiness, freedom, etc. and/or their opposites.
Here's the sort of thing I have in mind; contrast this with the opening paragraph of the Hemingway story:
The girl stood up and walked to the end of the station. Across, on the other side, were fields of grain and trees along the banks of the Ebro. Far away, beyond the river, were mountains. The shadow of a cloud moved across the field of grain and she saw the river through the trees.
Hope this helps!
Thank you so much for the help! I decided on "the yellow wallpaper, "the story of an hour," and "a jury of her peers". All three written of women in the nineteenth-century, hopefully I will get an A!! :) Although the symbols are very different, I believe the three authors were targeting similar hidden messages and used symbolism to convey their own personal feelings.