Phisicaly I would say food, water and oxygene, metaphysically I'd say fatality for nobody ever had a say in being alive. Now if you mean what makes us want to stay alive temporarily (cause then again there's the fatality of death) I would say the hope of leaving a positive footprint on a place that's also stuck in the spiral of fatality with us. NB: I've no clue, what on earth am I talking about. Thanks for reading.

The thing(s) that keep us alive are not the same things that give us purpose...unless our answer is God. ; )

For some people it is family; for others, work or career. For most people it's the necessity to feed, clothe and house yourself - this is fairly universal I think.