In-flight dietary requirements
Ultra-orthodox Jewish passengers, who do not trust the rabbinical supervision of airline meals, often bring copious quantities of home made food on board their flights.
I was made only too aware of this a couple of weeks ago when I sat next to two Jewish gentlemen, who were eating their own malodorous garlic sausage sandwiches throughout a flight from LAX to JFK.
(If only they had been eating LOX from LAX . . .)