It varies entirely by airline and union contract. Some airlines provide free meals for crew, some payroll-deduct for crew meals, some require crew to eat passenger meals and some mandate that crew pre-order specific meals.

I know of at least one security conscious foreign airline that ensures crew meals are obtained from two seperate caterers to prevent the possibility of contaminated or tampered food from a single source affecting the flight's safety. Others mandate that crew must only consume meals from approved sources in the hours immediately prior to or during a flight to prevent incapacitation.

Most American carriers have now shifted towards an "extra passenger meal" policy for crew (or a payroll deduct charge for special crew meals) with the only safeguard that captain and co-pilot specify different menu options.