weapon case
A type of portable case designed to safely store, carry and transport weapons (including the accessories) in concealed manner. It comes in various colours and shape, though rectangular is the most common one - as well as being made from various material (e.g. fabric, leather, or plastic).
Weapon case can be carried on back just like backpack (Danbooru post #5190996), or being handheld like a briefcase (Danbooru post #3566073). It can be soft or rigid container (Danbooru post #5334885). Some designs feature internal foam pad for extra protection (see Danbooru post #3702122).
This type of bag can also take shape as an instrument case (see Danbooru post #5947317 or Danbooru post #3958907).