Taking of company property OFF of the airplane is generally considered by many (most) airlines as a no-no.
The crew catering (of whatever type) is provided for your benefit whilst on duty, not after.
If a FD crew member (or, CC for that matter) continue to take catering OFF at the end of duty, these crew absolutely deserve to be warned one time only...if repeated, dismissed.
This is in many airlines written policy.
It really is that simple.
Generally, to remove catering from the airplane at the end of duty is considered theft of company property and crew should be handled accordingly.