public IReadOnlyList<PortalItem> PortalItems {get;}

{
  var activePortal = ArcGISPortalManager.Current.GetActivePortal();
  var owner = activePortal.GetSignOnUsername();
  var activeUserContent = await activePortal.GetUserContentAsync(owner);
  //Get content for a specific folder (identified by its folder id)
  //var userContent = await portal.GetUserContentAsync(owner, folderId);

  //Get all the folders
  foreach (var pf in userContent.PortalFolders)
  {
    //Do something with the folders

  }
  //Get all the content items
  foreach (var pi in userContent.PortalItems)
  {
    //Do something with the portal items
  }
}

{
  var packages = new List<PortalItemType>
  {
    PortalItemType.BasemapPackage,
    PortalItemType.GeoprocessingPackage,
    PortalItemType.LayerPackage,
    PortalItemType.LocatorPackage,
    PortalItemType.MapPackage,
    PortalItemType.ProjectPackage,
    PortalItemType.ScenePackage,
    PortalItemType.RulePackage,
    PortalItemType.VectorTilePackage
  };
  var folder = @"E:\Temp\PortalAPITest\";
  //Get the UserContent - refer to the initialization section above for more details
  foreach (var di in userContent.PortalItems.Where(pi => packages.Contains(pi.PortalItemType)))
  {
    var path = System.IO.Path.Combine(folder, di.Name);
    await di.GetItemDataAsync(path);
  }
}