Image Courtesy of SparkFun Electronics

Use an 8Ω speaker like this one to add sound to your project.  Don’t forget to use a current limiting resistor in-line with the speaker. You may need to solder wires onto the speaker terminals in order to use it. If you don’t have a soldering iron, you can use a piezo buzzer instead.

Buy a speaker from SparkFun or Adafruit.