Guitar Pick, or Plectrum
Choose a medium gauge to begin with (0.80-1.00mm).
An electronic one is best. You can find tuner apps for some ‘smart phones’.
Not essential when just beginning, but will be useful at some point. You can find metronome apps for some ‘smart phones’.
Not necessary to start with, but will be needed later.
Some means of recording your guitar playing. You could investigate recording on your computer, or finding a standalone recording device.
Use it always! It will prevent damage should you ever drop your guitar.
You can find a selection of these items here.