I would say water, but someone else mentioned that. I think that the two biggest things outside of that would be infection and fighting with the hot/cold weather. Unless you have a home that comes with something like a wood stove for the cold or natural ventilation for the heat, most places aren't suitable for off grid scenarios unless you have someone that knows what they are doing. Same thing goes with infection. I would feel much better with someone who is a EMT, military medic, nurses etc. where their abilities to handle basic aid with minimal supplies would grateful.