We once got prawn sandwiches on a Kosher flight. Profound apologies from yours truly to the pax who were utterly charming about it.
I personally sorted out catering for the return flight. A discreet tip from lead pax after landing suggested that the outbound blunder by the 'professional' caterers had been forgotten.
More recently, I have taken personal responsiblity to source Kosher snacks etc when required. The efforts have resulted in some suprise by the pax in question who brought their own food believing that GA might not make the effort to look after them.