Very old school:
Generic Vick's Vapor Rub. A dab under the nose helps with dry cough, nasal and chest congestion and annoying post nasal drip.

It is also good any time there are bad smells you can't stay away from. If society and normal life breaks down the smell of rotting garbage and raw sewage could be a constant. Cuts the worse of the smell of a rotting corpse.

Also has use in lighting fires and as a light grease.

Handy.