I can not live without it, without it I would die.

I can not live without it, i can not even try.

I can not live without it, its most important to me.

I can not live without it, I bet you would agree.

If I was stranded on an island, it's one thing i would need. 

If I was stranded on an island, I would need it indeed. 

If I was stranded on an island, I would go insane.

If I was stranded on an island, I would need to take my brain.