When you have a line of products that you always merchandise or package together, it is efficient to create an item as a composite object. You can group two or more items together in the 2D guidelines editor, and save them in the Catalog as one single object.
CREATE A COMPOSITE OBJECT
Simply follow the normal steps for adding an item, and choose "composite 2D object" as the item type.
From the item profile page of the composite object, you can directly edit your item by opening the editor. This will open it in a 2D guideline, on which you will be able to edit your composition:
Simply drag & drop a group of products on/off the shelf. Then save it as usual! Remember to activate the composite object before using it in your 2D guidelines, otherwise, you won't be able to retrieve it!