Surviving

Water
Despite the endless stream of dangers and horrors which a being is faced with upon first finding themselves in the Dungeon, after 24 hours most living creatures primary concern will be fresh water.

Water in the Dungeon is more valuable than silver or gold (but not more valuable than precious stones, which are used by the Grinder Dwarves to power their great machines). Denizens fight, and are often killed, over a bottle of water or for their turn at a trickle of drops leaking from a cave wall.

Some species which have adapted to Dungeon existence after many thousands of years take advantage of Denizen’s desperation for water by mimicking the sound of a flowing stream, such as the ever-bleeding Drought Beast.

Food
Although some species of smaller vermin (such as rats, fat grubs, and blind toads) do occupy the cracks and crevices, providing meager sustenance for trappers and foragers, the monstrous Denizens of Dungeon 26 are also well-aware of this fact and use it to their advantage. Certain long-term residents, such as the Adrenal Parasite, exploit their knowledge that tiny creatures such as rodents and beetles will almost always be consumed by significantly larger and more complicated creatures: namely, humanoids.

Child-Rearing
Author's note: I'll admit, this is going to be a tricky one to explain...