A ration card was a card issued by social workers to residents of Sanctuary Districts that was used to track food distribution at various points on Earth in the 21st century.
They were uniquely assigned to specific residents, but despite this ghosts often stole the ration cards of Sanctuary District A's weaker residents. (DS9: "Past Tense, Part I")
The ration cards were titled "Errand of Mercy Meal Program" (a reference to the TOS episode of that name). They also give the names of two San Francisco government officials: Dave Lister and Arnold Rimmer, a nod to the British television series
Since they had identification info for the resident to which they were assigned, it's unclear how ghosts were able to use stolen cards.