Methods for storing and preserving cannabis or cannabis-containing substances using container assemblies are disclosed. An exemplary container assembly includes a lid and a container body. The lid is configured to be closed onto the container body over an opening of the container body. The opening provides access to an interior space having a product compartment configured to store product. The assembly also includes a humectant compartment permanently secured within the assembly. The humectant compartment includes a rigid housing containing a humectant solution. The rigid housing is configured within the assembly to prevent leaking of the humectant solution into the product compartment while facilitating bidirectional transmission of moisture between the humectant compartment and the product compartment. The humectant solution regulates relative humidity of the product compartment to maintain the relative humidity at a predetermined level.