Was it left by former adventurers? A curious byproduct of the subterranean ecosystem?

Eat these so that you dont starve to death! The best way to use it is once you get a message that you're hungry; this consumes it fully and wastes no nutrition. Eating takes one turn.

Every ration of food keeps you alive another 1800 turns (compared to 1550 for a Mango). That's long enough to regenerate your health entirely six full times, or to recharge most staves three and a half times.