medicine box
This tag is currently connected with 薬屋行李 (kusuriya kouri, "medicine seller's wicker backpack"), a box with medicine (and possibly one's other possessions) carried on back, like backpack.
Usually made of willow or bamboo, but Medicine Seller in Mononoke and Ginko in Mushishi carry wooden medicine boxes.
Note that the pixiv tag 薬箱 contains some first aid kit box artworks.