Don't eat on the plane, even if the journey is 20 hours long (or 36 in one case).
Some of my best experiences have been from landing in a new country at 2 AM and looking for food, most notably in Beijing.
Something about the combination of hunger and jet lag gets you to go out and explore places you wouldn't. You'll see a side of the city you'd otherwise miss.
You might also get stabbed. Caveat emptor.