My dad has it set off by pork, caffeine, and tobacco smoke. Pretty interesting.
My stepson had them set off by excitement or stress. He had one every first day of school for years, had one prior to getting married, had them at birthday parties, sleepovers, etc. We tried all sorts of diet restrictions and nothing stopped them. He gets the terrible ones that Ginger mentioned, where he has visual impairment, vomiting and then he needs to sleep for hours and hours.