A
bottle cap for universal
retrofitting to one of a number of pre-existing beverage containers containing a beverage and having a removed cap and threaded aperture, having at least one container portion for containing at least one dispensable material, a threaded portion for receiving the threaded aperture and creating, when threaded, a water-tight
assembly; and a bag containing the dispensable material located in the container portion. Upon screwable attachment of the threaded aperture into the cap, the threaded aperture parses at least a portion of the bag to permit feeding of the material into the beverage. A plurality of such caps is also shown packaged for commercial sale. The material contained in the cap is selected from the group consisting of vitamins, medicaments, teas, flavors, concentrates and water-soluble
food material. Also shown is a universal cap further having a moveable aperture
assembly creating an open, fluid-flowing state and a closed, fluid-stopped state, having a top portion containing a drinking aperture and an elongated, moveable fluid-flowing portion. In accordance with another aspect of a dissolvable membrane encloses dispensable material in the cap, and the membrane dissolves upon contact with fluid in a fluid container to release the dispensable material into the fluid.