One key is to eat whatever you bring/buy, either in the airport or on the plane. Saving something for your next flight may attract the attention of the US Agriculture dog, sometimes generically referred to as Skippy the Wonder Beagle. Skippy doesn't want your lunch. Skippy just doesn't want your lunch to enter into the US. I'm never 100% sure on the rules, so I just eat my food on the SXM-US flight.