Store clicks in sequence

I am creating a game where the user is collecting 5 things out of the given 15 things in the environment.A collection is done by clicking on it.
I need to store the 5 things,the user collected IN THE SAME ORDER in which it was done.
This will be retrieved later in the game.
I have no problems with creating the environment and the onMouseDown() scripts…
Can some one plzzzzzzzz help me with how to save these clicks IN SEQUENCE?
and store WHERE?into XML? or use PlayerPrefs??or sumthng i am not yet aware of!
Thank you in advance!

Do they all use the same script attached to them? Then you could make a static list and just add to it. They stay in the order they get added. So you can get them out the right order to use (or save, or whatever).

using UnityEngine;
using System.Collections;
using System.Collections.Generic; //for the lists

public class NewBehaviourScript : MonoBehaviour 
	public static List<GameObject> Items = new List<GameObject>();
	void OnMouseDown() 
        //do whatever to pickup
		//add to list

If its different scripts write some managerscript that has the list and make the lists send to it when picked up.