Well it can't be only 1 thing , there are a number of thing we can't live without, but still there are three most important things , oxygen ; water and food ( it can be any type of food). And else are completely optional if we wish that we should have them then it's okay otherwise there is no problem when they are not there. But if water, oxygen and food are not available we all will die.
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But still imagine a life without oxygen and the most important thing is that we need it
wished WiFi should be free like oxygen :P 
It is an optional thing if we want it we should get it . And the necessary things are given to us already.
yes..If wifi would be free then.......hehe......Water,food,shelter is not free but
We cannot live without five important things--Air,water,food,clothing and shelter.Hence, they are necessary for survival and we can't do without them.
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