public IReadOnlyList<PortalItem> PortalItems {get;}

var portal = ArcGISPortalManager.Current.GetActivePortal();
var owner = portal.GetSignOnUsername();
var userContent = await portal.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
}

//user content previously from...
//var userContent = await portal.GetUserContentAsync(owner);

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\";
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);
}