first of all, I hope that you use SWWL_TOPLEVEL or make sure that you select only top level workitems in SWWL, deleting specific workitems ca lead to inconsistency in the system.
now for your questions: if a container element is available in the workflow but you can see it in a task it's usually a binding error. check the binding to the reminder mail.
as for adding more data to the workitem, you will probably need to enhance the object, adding more attributes to get the data to the workflow container. for this you will need some knowledge of ABAP and workflow so I would recommend you call on an expert if you can. if not maybe this will help: Enhancing Object Types: Inheritance and Delegation - SAP Business Workflow: Reference Documentation - SAP Library.