Devices and a method for releasing gas in a container after closing and sealing to pressurize and/or prevent or counteract buckling thereof, and or provide structural rigidity and strength thereto and or release components. The method introduces a reactive agent into the container after filling and before sealing. The reactive agent is controlled to react to provide a gas and optionally components, which a) provides a positive pressure to prevent or counteract buckling and provide structural rigidity to the container, and b) and or changes the state or characteristics of the headspace and or contents of the closed container. The devices include a closure, a cap and a container. The reactive agent is brought to chemical reaction by moistening, heating, catalyst and the like. The closure includes the reactive agent and is disposed in the container. The external trigger is a device that emits energy that provides heat to the reactive agent to stimulate the chemical reaction.