Someone is murdered on the cruise ship you're on. Passengers are told to lock themselves in their cabins and await instructions. The captain speaks from the ships PA system, "The first contestant has fallen. Only 5,132 remain." With that, the doors all click and swing open.
As magic returns to the world, purchasable drinks actually start having magical effects. Energy drinks actually imbue you with energy. Diet drinks cause noticeable weight loss. Vitamin drinks heal injures and disease, and so on.