Main things that kill you in grid down emergencies and disasters

Dysentery-

Pneumonia - Lung infections.

Wounds - either from

 

Dysentery - Killed most soldiers in the American civil war and many other wars and disasters.

Pneumonia - Caused by many upper respiratory infections.

Wounds - Uncontrolled bleeding.
Wounds - Infection and Blood sepsis.

Exposure

Having good sanitation and clean water in a disaster is important. Typhoid, cholera, Hep A seem to run wild in disaster situations.
Avoid crowded situations and be out of cities if you can.

Bleach, soaps, and anti bacterial detergents should be stocked.
Anti dysentery medications and treatments should be stocked.
Water filters and water treatments stocked.

Lung infection salt treatments and antibiotic medications should be stocked.

Wound closure equipment and ability to stop bleeding.

Keeping old antibiotics is better than having no antibiotics to prevent wound infections spreading.

Stocking emergency food supplies and vitamins to maintain health, most diseases take hold when people are weakened by malnutrition.

If you can treat or prevent these main things you have a very high chance of survival in emergency or disaster.