In addition to the previous poster who has drawn attention to the plant, you might want to think about a certain phrase that is repeated throughout the play: "eat your eggs". Bit of an odd symbol, you may be thinking, but bear with me. This phrase first occurs quite early on in the play in the form of an order from Ruth to Walter to shut him up. Walter then goes on to reinterpret the phrase to demonstrate how women impede men from accomplishing their aims - Walter claims that every time a man becomes thrilled by something, a women tries to "calm him down" by telling him to eat his eggs. Thus, thinking about the context of the play as a whole, shutting up or being stocial and eating your eggs symbolises the kind of acceptance and stoicism in response to adversity and problems that Walter and the rest of his family certainly confront in their lives. Walter of course sees Ruth (who is making his eggs) as an impediment in the way of him accomplishing his dream, and he tries to argue that she should be more encouraging. The eggs that she cooks him every day represent her somewhat robotic approach to supporting him. She does give him sustenance, but every day this is in the same, repeated fashion.
That is a major one, but you also might like to consider how Beneatha's hair becomes a symbol of her identity. Go back and read the play and consider how her hair changes in style and why. Hope this helps!
One of the symbols in A Raisin in the Sun is Mama's straggly plant. She wants to take this to the new house, although she plans to have a much more successful garden there, because this plant "expresses ME" Though the plant has struggled to live and seems to lack the beauty for which it would ordinarily be valued, it is significant to Mama because it has survived despite the struggle, as her family has survived.