Neccessary or Unneccesary?

Can anyone tell me what are the necessary items that you couldn't do without and what you could have really done without or was just a waste of money? For example one of my coworkers told me that the diaper genie is the biggest waste of space you could ever ask for lol. Any other suggestions? I am only 21 weeks 1 day but I'd like to start my registry at around 25-30 weeks. (I am making a list lol) thanks everyone