As you can see, if you arrange the cans in 5 rows, alternating 4-3-4-3-4, you will achieve a smaller perimeter and area than with either of the two rectangular packing arrangements. This helps reduce the amount of shipping materials needed.
If you have a hexagonal arrangement with k rows of alternating length, in which the length of the longest row is n, then
perimeter = 2n + √3k + 2 - √3
area = n[(√3/2)k + 1 - √3/2]
If you have a hexagonal arrangement with k rows of equal length n (aka staggered), then
perimeter = 2n + √3k + 3 - √3
area = (n + 1/2)[(√3/2)k + 1 - √3/2]
(Both formulas assume the diamter of each circle is 1. If the diamter is d, multiply the perimeter formula by d and the area formula by d².)