Choose the internal arrangement first
Place the products in the intended order and measure the full arrangement. Include space for lifting each item out and any supporting insert, ribbon pull or tissue. A box that looks compact in a drawing may be awkward to unpack if there is no room for a finger beside the product.
If the contents change across several versions, share each version before a common box size is selected. A shared outer box with different inserts may be useful, but the feasibility and economics should be compared with separate formats.

