In Season 6, Episode 8 of Game of Thrones, Cersei seemingly lost her last hope when Tommen outlawed trials by combat.
For a moment it seemed she had no more moves left – and then this little exchanged happened between her and Qyburn.
There's a really good chance he was talking about the caches of wildfire stashed around the city from Mad King Aerys's reign.
Bran's vision focused on them for a reason – and this could be it.