Rationing is carefully controlling the amount of something that people use. During World War Two, Americans participated in the rationing of food, gasoline, and other materials.
When something is in short supply, like rubber and metal during the Second World War, a government will often institute rationing to save that material, making sure there's enough of it for emergencies. Rationing during the war meant that people had a specific amount of food they could buy each week, and once an item was used up, they had to wait until they got a new ration book to buy more. Ration means "hand out in fixed amounts."