I too have often wondered what the Cocoa Unit was, which is mentioned in the various Manuals. I checked my Medical Supply Catalog, and couldn'd find anything which looked like it could be a Cocoa Unit.
However, I remember some time ago seeing an Aid-station Beverage Pack, which I believe could be the item. The photo below shows the pack, and I have also included a short description about the pack:
The aid-station beverage-pack supplement was designed for application at forward-area aid-stations as supportive subsistence for battle casualties and exhaustion cases. Interest of the Laboratory in the initial development concerned the assembly and packaging of components designated by The Surgeon General. Components included coffee, tea, cocoa beverage powder, evaporated milk, and sugar. Accessory items included plastic sippers, a can opener, and toilet paper. As ultimately developed, the supplement provided ingredients for the preparation of 290 twelve-ounce drinks.
A forerunner of the supplement was the B-C (Battle-Casualty or Bouillon-Cigarette ration) kit containing cigarettes, bouillon cubes, and matches. The packaging of the B~C was assigned to the Laboratory in 1944. Field experience revealed that the kit was inadequate as far as providing desired hot drinks and it was recommended that a new pack, containing coffee, cocoa, sugar, bouillon, and paper cups, form the basis for a new specification. Approximately 9,000 cases of the aid-station pack were procured before the end of 1945.
The ration was standardized for issue to ground battalion aid stations in 1944 and ever since then has maintained a "standard item" classification. Postwar interest in the ration was casual although it must be noted that a Marine Corps research report, completed just as the war ended, indicated that the aid station had potential peacetime use. The report agreed that the pack did "not represent an essential item during peacetime," but suggested applications in maneuvers, by airplane crews and rescue craft, and for parachute supply to isolated units.
I can't say for sure that this is the Cocoa Unit that is referred to in the manuals, but I have a strong suspicion that it either is the unit, or replaced it later on in the war.
Hope that helps,