Episode 7 of Koutetsujou no Kabaneri brings up the point that nobody in Japan eats rice anymore, since the rice paddies are outside the stations, and hence overrun by the kabane.
This makes a lot of sense, and is a splendid bit of worldbuilding. But if they can't grow rice, what staple food(s) do they grow and eat instead?
Out of all the common staple foods currently eaten, it seems that potatoes (or sweet potatoes) can provide the most calories-per-unit-area, clocking in at about 4-5 times as much as rice. But at just 4-5 times rice's calorie/area yield, they'd have to have lost no more than 75-80% of their arable land to maintain the same calorie output. Judging from the sizes of the stations we've seen, it doesn't seem plausible that they still have that much arable land - we see the railforts driving through days of outside-station land between stations.
Perhaps the resolution here is that Japan's population has dipped so precipitously in the face of the kabane menace that the meager amount of land enclosed by the stations does suffice to grow enough of some other staple crop to feed the people?