How can I create a chest that opens on click?

Great model. Here is what I would do in C# (this is untested, but should work).

This is the no frills way to do it...

 using UnityEngine;
 using System.Collections;
 
 public class OpenCloseChest : MonoBehaviour {
 
     public bool isOpen;
 
     void OnMouseUp(){
         isOpen = !isOpen;
     }
 
     void Update(){
 
         if(isOpen)
             {
             animation["Open"].wrapMode = WrapMode.Once;        
             animation.Play ("Open");
             }
         if(!isOpen)
             {
             animation["Open"].wrapMode = WrapMode.Once;
             animation.Play ("Close");
             }
     }
 }

But this would play either animation whenever the chest was opened, so it would be advisable to add a timer to control when the chest is opened.

 using UnityEngine;
 using System.Collections;
 
 public class OpenCloseChest : MonoBehaviour {

         float openCloseTimer;

         public float setOpenCloseTimer;
         public bool isOpen;
 
     void Awake(){
 
         openCloseTimer = 0
 
     }
 
     void OnMouseUp(){
 
         if(openCloseTimer <= 0)
             isOpen = !isOpen;
 
     }
 
     void Update(){
 
         openCloseTimer -= Time.deltaTime;
 
         if(openCloseTimer <= 0)
             openCloseTimer = 0;
 
         if(isOpen)
             {
             animation["Open"].wrapMode = WrapMode.Once;
             animation.Play ("Open");
             openCloseTimer = setOpenCloseTimer;
             }
 
         if(!isOpen)
             {
             animation["Close"].wrapMode = WrapMode.Once;
             animation.Play ("Close");
             openCloseTimer = setOpenCloseTimer;
             }
 
     }
 }

The final issue is that the script above, while limiting how quickly the chest could be open or closed, does not limit the distance from which the player could open so-said chest. So, the final addition is to check the distance the player is from the chest and then enable the ability to open it.

 public class OpenCloseChest : MonoBehaviour {
 
         public float distanceToActivate;
         public float setOpenCloseTimer;
     
         float distance;
         float openCloseTimer;
 
         bool isSwitchable;
         bool isOpen;
 
         GameObject player;
     
     void Awake(){
 
         isSwitchable = false;
         openCloseTimer = 0;
         player = GameObject.FindGameObjectWithTag("Player");
 
     }
 
     void OnMouseUp(){
 
         if(openCloseTimer <= 0 && isSwitchable)
             isOpen = !isOpen;
 
     }
 
     void Update(){
 
         distance = Vector3.Distance(this.transform.position, player.transform.position);
         
         if(distance <= distanceToActivate)
             isSwitchable = true;
         else
             isSwitchable = false;
 
         openCloseTimer -= Time.deltaTime;
 
         if(openCloseTimer <= 0)
             openCloseTimer = 0;
 
         if(isOpen)
             {
             animation["Open"].wrapMode = WrapMode.Once;
             animation.Play ("Open");
             openCloseTimer = setOpenCloseTimer;
             }
 
         if(!isOpen)
             {
             animation.Play ("Close");
             animation["Close"].wrapMode = WrapMode.Once;
             openCloseTimer = setOpenCloseTimer;
             }
 
     }
 }

Hope that helps!

A.