I stock the Grand Champion (Granchan Series) of 1:64 die-cast cars. Each release includes six car models with two colour variants (so, that's 12 in total), and apparently a "secret" car.

They are randomly packed into small boxes that resembled those small cereal boxes you took on holiday, then randomly packed into larger boxes of 12. Since the boxes are sealed and identical, there's no way of me knowing which is which, although I've recently been told a master box of 12 contains each piece!