this invention relates to containers that include at least one sub - container and to methods and / or systems for mixing first and second substances responsive to opening of the containers and the at least one sub - container that is included therein . the invention advantageously provides methods , systems , containers , sub - containers , seals and / or tethers that may be used in storing first and second substances in an unmixed state , until it is desired to mix the first and second substances just before utilization thereof .