to access files in future
string key = Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.Add(storageFile);
//save this key for access file later
//Access file from saved key
StorageFile file = await StorageApplicationPermissions.FutureAccessList.GetFolderAsync(key);
if you have too much file you can add StorageFolder of files
string key = Windows.Storage.AccessCache.StorageApplicationPermissions.FutureAccessList.Add(storageFolder);
StorageFolder folder = await StorageApplicationPermissions.FutureAccessList.GetFolderAsync(key);
then get StorageFiles from the parent StorageFolder
StorageFile childFile = await folder.GetFileAsync("filename");