Checklist:
1. vitamins, meds (in small ziplocs; by day).
2. security pouch for passpt, currency.
3. contingency items (e.g.,extra cold or warm weather colthing, Pepto-Bismol, ibuprophen, travel insurance papers, emergency telephone numbers, etc. ).
4. electricity conversion device (a converter, not just an adaptor).
5. open mind (yes, they may be different, but probably polite and curious just like you).
6. spare media (SD/CF/uSD cards), various DLSR lenses, camera manual (you'll be jet-lagged).
7. Beforehand: adjust your schedule to the destination time zone. DC to San Francisco is relatively painless; DC to Honolulu is kinda unsettling, DC to Japan is painfully disorienting:
Time Zone Event Planner - Compare Multiple Time Zones
8. Plan your departure logistics (parking lots, rental car vs. personal auto comparison, coupons, airport layout info) at:
http://www.metwashairports.com/
9. Flexibility - 41 years doing this, something *always* goes wrong, every time. E.g., last week I checked a rental car into Avis Albuquerque, and they assured me I had not rented the car from them (I had). In Rome, my wife and I missd our connection due to hand-carried luggage issues. Plan on this, roll with it. Humor is essential; we're all human.
10. Pack 2 ~ 3 days before your departure, put a special marker on your luggage (I've had people pick up my bags; they all look alike).
11. Enjoy this time in your life. You will look back on it and smile in 2020.