What do Gregor's alarm clock, window, food items, and couch symbolize?
This is tricky because objects can be very different kinds of symbols to different people, but I will try to get you started with some ideas that come to my mind.
A clock is a good symbol of time passing, isn't it? That might be one kind of symbol. Another idea is that an alarm clock symbolizes the control that others have over our lives. For example, the alarm clock forces us to get up to go to school, go to work, etc.
The window is a very powerful symbol. It can represent freedom or imprisonment. If you are looking out, but are trapped inside, it really represents both, doesn't it?
Food is a very emotional symbol for many people. Have you ever heard the expression "comfort food"? Food represents our parents feeding us, and it also represents life because we cannot have life without it.
The couch is probably the most difficult symbol for me. Could it be a symbol of laziness for you?
I hope this helps you to get started writing your sentences. Good luck!