How long is "very long"? And what sort of country will you be riding in?
Things I'd add to the above:
1) If you don't know the country, a GPS and/or map would be useful.
2) If there's any chance you'll be out after dark (or trailering, etc), one of the LED lights on a headband is a lot handier than a conventional flashlight.
3) Cell phone may or may not be useful, depending on whether you're likely to have coverage. (Where we ride, it'd only be useful as a camera.)