During the Second World War, you couldn't just walk into a shop and buy as much sugar or butter or meat as you wanted, nor could you fill up your car with gasoline whenever you liked. All these things were rationed, which meant you were only allowed to buy a small amount (even if you could afford more). The government introduced rationing because certain things were in short supply during the war, and rationing was the only way to make sure everyone got their fair share.
This is the book issued to me when I was 16 years old in 1943.