There are still people who don't have such stores of food though. But sure, another example is a pedestrian with a gas can arriving at a gas station. The point is there are many things that are necessary for modern existence, yet there's a competitive market of not-completely-powerless actors keeping prices in check for the nearly-powerless ones. Healthcare is an outlier by being an extreme market failure, through both not enough regulation and too much regulation (that is to say, corruption).

(Although maybe with the rise of big surveillance and fine grained price discrimination we'll start to see these situations in other markets get exploited more)