Arrange smaller boxes inside the larger box to divide up the area. Choose which sections will be allocated for flowers and which will have macarons.
Place a layer of tissue paper in the section which will have flowers, then line it with your plastic bag. Make sure this is completely water tight and has no holes.
Cut the foam brick to size so that it neatly fits within the space allocated to flowers.
Pour some water over the foam block, ensuring that it is thoroughly soaked.
Cut the flowers to size by trimming the stems so that the base of the flower rests on top of the foam brick. If you plan to store the box with the lid on top, endure that the flowers do not sit any higher than the top edge of the box.
Line the remaining cavities with tissue paper and then fill them with macarons. If the box is too deep you can put a layer of rice underneath the macarons so that they sit higher.
Wrap the macaron boxes in a layer of cellophane to ensure they are completely seeled from the flowers.
Store the box in the fridge until you are ready to gift it.