As noted, in a post-zombie apocalypse (PZA) scenario, chemicals and equipment will likely be scarce.
This leaves us with what can be scrounged or easily (relatively) made.

For prints: salted-paper and its variants (albumen, casein etc.,), cyanotype, VDB are all very DIY and do not demand super high-purity materials.

Camera negatives: Collodion would be hard to find/make, but a slow ortho silver-gelatin emulsion could be made without fancy equipment or exotic chemistry. It doesn't even have to be coated on glass or film (paper works), and gelatin can be replaced by other colloids. Easy - yes! Fast with latitude - No!


Making a slow but usable silver-gelatin emulsion is NOT difficult. Making a faster emulsion requires a bit more precision and technique.
Further increasing speed, controlling the curve shape, adding spectral sensitivity, latitude, acutance, anti-halation, etc., etc., each add complexity, demand high-quality ingredients, and demand precise methods.

Just in case, you might want to stash a few boxes of film and some developer before the zombies arrive.