The chief medical officer aboard Federation starships could issue diet cards with specific nutritional requirements for individual crewmembers. In 2266, Doctor McCoy changed Captain Kirk's diet card to include dietary salad, as Kirk's weight had gone up a bit since his most recent physical. (TOS: "The Corbomite Maneuver")
In 2268, Nurse Christine Chapel passed out several of these cards to the Starnes Exploration Party orphans so they could have whichever ice cream flavor they wanted, such as coconut and vanilla, chocolate wobble and pistachio, or peach. (TOS: "And the Children Shall Lead")
The diet card was visually identified in conjunction with the script notes for "The Naked Time" final draft script.
The cards used in "And the Children Shall Lead" were identified on-screen only as "cards", while the props themselves were identified in the shooting schedule as "program blocks".