Water is essiential to life, and in many cases will be the heaviest part of any pack, whether for planned outings and adventures or emergencies.
A great deal therefore depends on the terain.
Non drinkable water is found most everwhere in urban or suburban areas, therefore little need be carried, only means of purification.
Butane lighters are lighter than most alternatives, and suitable for all but the most extreme conditions.
Lithium batteries are lighter than alkaline and give exended service.