Put the cake on a serving plate or cake board and spread the sides with the apricot jam, reserving a little.
Knead the red icing until softened, then roll out thinly on a surface lightly dusted with icing sugar. Cut out 2 rectangles, 19 x 16 cm (7½ x 6½ inches), and press them on to the long sides of the cake. Re-roll the trimmings and cut out 2 x 13 cm (5½ inch) squares. Press them on to the short ends of the cake.
Smooth the icing over the cake and press the icing joins together. Don't worry if the icing sags down the sides – this will make the sack look more interesting. Smooth the top edge of the icing to give a wavy effect, then fill the top of the sack with sweets and coins. Roll out the white icing and stamp out tiny stars or holly leaves. Stick them on to the sides of the sack with a little jam.