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 Mimic in the rather unconventional form of a weapon, can be used as a weapon and grows more powerful over time. If introduced to the party early it could make an unexpected betrayal. Skittering around like a terrifying insect.