The mechanisms of rationing had been prepared before the declaration of war, consequently, when war was declared rationing was only a few days behind. It was controlled by the Ministry of Food and administered by a complex system of points and clip-out coupons found in the ration books that were issued to every person, children and adults alike. Almost everything, from food and furniture, to clothing and shoes had to be purchased with a combination of coupons and cash. Your new suit may have borne a price tag of five pounds, but if you did not have the requisite number of clothing coupons, you could not purchase the suit. The same restrictions applied to all consumer goods.
About the only unrationed food was what you could grow yourself. Parkland and lawns were planted with food crops, everyone had a garden. That which could not be home grown had to be imported at great risk by the merchant navy. Certain items, such as tropical fruits, became completely unavailable. Other staple foods, milk and eggs for example, were most readily available only in dried form as it was much easier to transport and had far better keeping qualities Refined flour also became a thing of the past. It was replaced by "National Flour", which was completely unrefined and produced a heavy, gray loaf of bread. Naturally enough, given the uncooperative nature of the flour and the shortage of eggs, sugar and butter, fancy baking became little more than a fond memory.