SingleCharacterScript

using UnityEngine;
using System.Collections;
public class SingleCharacterScript : MonoBehaviour
{    public class Stuff{        
        public int bullets;        
    public int grenades;        
    public int rockets;        
    public Stuff(int bul, int gre, int roc)        {
            bullets = bul;
            grenades = gre;
            rockets = roc;
        }
    }    
    public Stuff myStuff = new Stuff(10, 7, 25);    
    public float speed;    
    public float turnSpeed;    
    public Rigidbody bulletPrefab;    
    public Transform firePosition;    
    public float bulletSpeed;    
    void Update ()    {
        Movement();
        Shoot();
    }    
    void Movement ()    {        
        float forwardMovement = Input.GetAxis("Vertical") * speed * Time.deltaTime;        
        float turnMovement = Input.GetAxis("Horizontal") * turnSpeed * Time.deltaTime;
        
        transform.Translate(Vector3.forward * forwardMovement);
        transform.Rotate(Vector3.up * turnMovement);
    }    
    void Shoot ()    {        
        if(Input.GetButtonDown("Fire1") && myStuff.bullets > 0)
        {
            Rigidbody bulletInstance = Instantiate(bulletPrefab, firePosition.position, firePosition.rotation) as Rigidbody;
            bulletInstance.AddForce(firePosition.forward * bulletSpeed);
            myStuff.bullets--;
        }
    }
}

Inventory

using UnityEngine;
using System.Collections;
public class Inventory : MonoBehaviour
{    public class Stuff{
    public int bullets;        
    public int grenades;        
    public int rockets;        
    public float fuel;        
    public Stuff(int bul, int gre, int roc){
            bullets = bul;
            grenades = gre;
            rockets = roc;
        }        
    public Stuff(int bul, float fu){
            bullets = bul;
            fuel = fu;
        }        
    // Constructor
    public Stuff (){
            bullets = 1;
            grenades = 1;
            rockets = 1;
        }
    }    
// Creating an Instance (an Object) of the Stuff class
    public Stuff myStuff = new Stuff(50, 5, 5);    
    public Stuff myOtherStuff = new Stuff(50, 1.5f);    
void Start(){
        Debug.Log(myStuff.bullets); 
    }
}

MovementControls

using UnityEngine;
using System.Collections;
public class MovementControls : MonoBehaviour
{    public float speed;    
    public float turnSpeed;    
    void Update (){
        Movement();
    }    
    void Movement (){        
        float forwardMovement = Input.GetAxis("Vertical") * speed * Time.deltaTime;        
        float turnMovement = Input.GetAxis("Horizontal") * turnSpeed * Time.deltaTime;
        
        transform.Translate(Vector3.forward * forwardMovement);
        transform.Rotate(Vector3.up * turnMovement);
    }
}

Shooting

using UnityEngine;
using System.Collections;
    public class Shooting : MonoBehaviour
{    public Rigidbody bulletPrefab;    
        public Transform firePosition;    
        public float bulletSpeed;    
        private Inventory inventory;    
    void Awake ()    {
        inventory = GetComponent<Inventory>();
    }    
    void Update ()    {
        Shoot();
    }    
    void Shoot ()    {        
        if(Input.GetButtonDown("Fire1") && inventory.myStuff.bullets > 0)
        {
            Rigidbody bulletInstance = Instantiate(bulletPrefab, firePosition.position, firePosition.rotation) as Rigidbody;
            bulletInstance.AddForce(firePosition.forward * bulletSpeed);
            inventory.myStuff.bullets--;
        }
    }
}