Accessing a variable of a script from another scene.

I'm using static vars to hold things like points, lives, health etc. These variables are defined in a script called Control.js, and they may be accessed as Control.points, Control.health etc. This script is attached to my player (a FPS controller), and their static variables survive during the whole game:

 static var gunRange: float = 100;

Another alternative is to keep these variables in a script assigned to an empty object, and include the DontDestroyOnLoad instruction in its Awake function:

 var gunRange: float = 100;
 
 function Awake () {
     DontDestroyOnLoad (transform.gameObject);
 }

EDITED: If you want to use the static variable alternative, your scripts should look like below:

The ShopMenu.js script:

 function OnGUI () { 
     
     GUI.Box (Rect (10,10,250,90), "Shop Menu");
     if (GUI.Button (Rect (20,40,200,20), "Longer Range:   15 Points  ")) {
         Debug.Log ("Bought Longer Range");
         BuyRange();
     }
 }
 
 function BuyRange() {
 
     if (Points.score>=15){ // if the player has enough points...
         shoot.gunRange = 50;  // buy the new range...
         Points.score -= 15;  // and subtract the points spent
     }
 }

The shoot.js script:

 var bullet : Rigidbody;
 static var gunRange = 40;  // this variable may be accessed anywhere as shoot.gunRange
 
 function Update () {
 
     if (Input.GetKeyDown ("space")) {
         var clone : Rigidbody;
         clone = Instantiate(bullet, transform.position, transform.rotation);
         //Give the cloned bullet velocity along z axis
         //(is it correct? the bullet will go the Up direction of the turret!)
         clone.velocity = transform.TransformDirection (Vector3.up * gunRange);
     }
 }

The Points.js script:

     static var score = 0;  // this variable may be accessed as Points.score anywhere
     
     function OnTriggerEnter ( other : Collider ) { 
     
         if (other.tag == "Points") { 
             score += 5; 
             Destroy (other.gameObject); 
         } 
     }
     
     function OnGUI (){ 
     
         GUI.color = Color.red; GUI.Box (Rect(25,25,100,30), "Points: "+score); 
     }
     
     function Update () {
     
         if (score==15) {
             loadShopMenu();
         }
     }
 
     function loadShopMenu () {
 
         yield WaitForSeconds(3);
         Application.LoadLevel(2);
     }