Thank you for your question.
Usually we recommend that your Application should not cause full navigations but use the HTML fragment navigation model in WinJS. This allows you to keep in memory state and is preferred because of performance reasons.
Check out the following sample if you are interested in Navigation through WinJS fragments http://code.msdn.microsoft.com/Navigation-with-Fragments-5e4990f5/sourcecode?fileId=43855&pathId=53202417
If however, a full navigation model still makes sense for your application you can store data using Windows.Storage.ApplicationData, more information @
http://msdn.microsoft.com/en-us/library/windows/apps/hh465118(v=VS.85).aspx
Thanks,
Harris
Harris