I´m not sure but i thik the answer is "NO, you cannot use an activity inside a panel.
BUT this should not stop you to use you one activity wisely
For example;
You can get a list of products in create (http with json-answer) and save the list (you got in JobDone) in a processglobal variable or you save the list to an sqlite-database or you use the list to build a scrollview or listview. The user then can select one of these products and click a save-button. A new http-job sends the new product to your server where you can put the product in a shoppingcart or whatever you want to do with it ;-)
For some things you dont need a new activity but for some you do need it...
Activities are the Android-Way of handling "Forms" like in Delphi/Windows. That i had to learn too ;-)