A cap for bottles that allows the user to select one or more additives. A base has an axis with a coaxial cavity, typically threaded, for attachment to the bottle. A housing rotates and reciprocates on the axis. A mechanism biases the housing from the base on the axis in a storage position. Pushing the housing against the biasing mechanism moves the housing to an operative position. Compartments arranged in a circle around the axis inside the housing hold the additives. An opening in the compartment bottom is covered by a frangible seal. As the housing rotates, the compartment openings align with an aperture in the base that extends into the cavity. Sharp spikes extending from the aperture puncture the seal when the housing is pushed to the operative position, thereby creating a hole for the additive to flow into the bottle.