Generating random world point to spawn object

Hello everyone. I have a large open world and I want to spawn items at random spots. What I figured I would do is find a random x/z point and do something like this:

function Respawn(){
	yield WaitForSeconds(1);
	Instantiate(item, Vector3(randX,50,randZ), transform.rotation);

The levels consist of only a water plane so the X/Z coords just need to be somewhere on the grid. My question is how do I generate a random coord?

The Scripting Manual is a very good thing to read. Your code is here: