I crack heavy hydrocarbon molecules into lighter useable products like gasoline diesel and jet fuel. Some days take the sulpher of the products. I would say that it would only be a matter of days before society was turned upside down if we all dissapeared. Power Plant or grid operators would be felt even faster! Nurses, police officers, firemen, all the jobs that require 24/7 coverage in my mind are the most productive to society. Or they allow others to be productive by keeping the lights on and the streets safe.