These tokens were part of the "carrot and stick" program in the many forced labour camps under organized by KL Buchenwald, workers that made a certain quota for example were given these tokens with which they could buy extra food in the camp canteen.
Also concentration camps were for a part run like ordinary prisons, those inmates that weren't detained under "Nacht und Nebel' decree could sometimes write letters to their family, they also could receive food parcels and money from their family, with the money they could buy stamps for the letters they could sent or buy a small amount of extra food in the camp shop.
These small things like being in contact with your family and getting a small supplement to your daily ration could mean a lot for a concentration camp inmate, those that were detained for resistance activities usually couldn't benefit from these official privileges and they had to rely on the camps resistance group, usually led by the communists, for that little something extra to make their detention a bit more torrable.
My greatgrandfather, who was detained in a forced labour camp, Reimagh Kahla (an underground factory for Me262 jets), from May 1944, a camp under LW control but with a concentration camp regime.
He was in contact with his wife and son until they were liberated in early Oktober 1944, in that time his family also sent food parcels and even work clothing to him.
These forced labour camps were perverse, those in charge of course didn't care at all about the welfare of those detained, they were enemies of the nazi state and they deserved to die anyway but the more the inmates got from there families, the less the camp organisation had to provide; people that work need a minimum of food and supplies to keep them going.
The system to force the inmates to work was also rather easy, besides beating them, their food ration was based on what they produced and if you didn't get your quota you wouldn't get your full ration; not eating enough means that you get weaker every day and once you were in that downwards spiral it meant you were as good as dead.