Health Bar Help (2d, Unity 5)

I have a script for a health bar but I need some help with the follower:

• Display a canvas (game over menu) when the bar reaches 0

• Refills health by 80 points when the player collides with a game object.

P.S. Also, if anyone could provide help with code to kill the play on contact of a certain object (detected by tag) and brings up a menu (not entirely necessary), that would be fantastic. All the tutorials online come with problems (probably because their all Unity 4.6 and below).

Code:

 using UnityEngine;
 using System.Collections;
 
 public class HydrationBar : MonoBehaviour {
 
     public float max_Health = 100f;
     public float cur_Health = 0f;
     public GameObject healthBar;
 
     // Use this for initialization
     void Start () {
         cur_Health = max_Health;
         InvokeRepeating("decreaseHealth", 1f, 1f);
     }
     
     // Update is called once per frame
     void Update () {
     
     }
 
     void decreaseHealth()
     {
         cur_Health -= 5f;
         float calc_Health = cur_Health / max_Health;
         setHealthBar(calc_Health);
     }
     
     public void setHealthBar (float myhealth)
     {
         healthBar.transform.localScale = new Vector3(myhealth, healthBar.transform.localScale.y, healthBar.transform.localScale.z);
     }
 }