Stones that have been attuned to the extreme temperatures of deserts or icy wastes. Such stones are quite valuable to adventurers as they can use them in order to preserve or prepare meals, make extreme environments bearable, and use them in clever devices.
Nuclear war, zombie outbreaks, meteor strikes, economic collapse, alien invasion, no matter how it happens an apocalypse makes for a unique and engaging setting to run a campaign in, even for a jaded GM.
Here’s a few quick tips that can make a good zombie or other post apocalypse game a great one, and keep the group coming back (from the dead?) for more.
A cult's theology is binding on the god involved: it is possible for that god to believe (and see, just like Winston Smith in 1984) that other gods are mythical, or jumped-up demons, or failing older spirits, even while those gods actually exist and thrive and act in the cosmos, even while working against him.