Depends on how much you use your moped. If need it for primary transportation everyday, spares make sense.
If you only ride in for recreation just get a spare spark plug or two and a small tool kit with a spark plug wrench.
Also maybe some tail light bulbs and a small container to carry some 2 cycle motor oil, in case you have to gas up on the road.
A mobile phone is a good accessory also in case you get stuck and need someone to rescue you. You can also talk on it while you ride to impress all the SUV drivers who are doing the same thing when they run you off the road.