Abstract: The inventions relate to containers that store liquids and/or particle solids and the removable caps that are used to stop contents from leaving the containers when the cap is in a closed position and to allow contents to be poured from the container in an open position. The caps may be used in a system that includes containers designed to stack together or to be otherwise stored together in a manner that minimizes the storage space required for such containers. The caps may include a base and a nipple having a low profile such that the top of the nipple does not protrude beyond the top of the base. The base may include a counterbore that is sufficiently large in diameter to allow the nipple to be grasped when in a closed position. The present inventions may be practiced with a stopper that interacts with the nipple to close the path through which fluid may flow.