I did an extended XC across the US on a Piper Archer, and also did an extended trip (1+ year) on a motorcycle... w/ surprisingly a lot of similarities in planning, etc.
- Be flexible... have a general plan / idea but keep your options open. Once underway I rarely planned more than 1 day ahead.
- Weather changes rapidly... I got weather briefings before every flight but still had to divert mid-flight twice! FSS is your friend.
- Give yourself extra time... maybe schedule extra days as buffer. Get-there-itis kills.
- (On my last day I had to wait out a thunderstorm through the night before flying the last leg home -- already tired -- just to return the rental "on time". Very stupid of me!)
- Do consult locals, but be skeptical at the same time. Lots of yahoo pilots out there.
- If possible, schedule some non-flying days and rest up.
- Be mindful of maintenance schedules, oil changes, etc.
In summary... 1) we tend to grossly underestimate the time required to complete extended trips; and 2) weather is king, it will dominate any plan.
For my XC, I didn't bring anything special (other than what's normally in my flight bag + extra maps). Some clothes, camera/laptop, that's it.