I've done 50 miles SS before, I think I could do more but that was my longest ride so far without gears.

Bring:
- water
- snacks
- money
- a tube or two
- a pump
- tire levers (if you can't mount a tire without them)
- a wrench to remove your wheels (if you don't have quick release)
- an allen wrench set
- anything else you feel you may need.