This is the standard singleton I use for basic data in Unity games.

GameManager.cs

/*
 *  Game Manager
 *  This is how we will save our persistent data such as: 
 *  Logged in save data from a json file and assigning variables which we access in game
 *  With this Singleton we can store data we need for later use
 *  Example on how to use: GameManager.Instance.[Variable Name / Method Name]
 *  Methods and Variables must be public
 *  Note: A new singleton should be created per platform for achievements string literals and specific achievement methods 
 *
 */

/// Note: that the more namespaces we use the more loading this screen has to do
using UnityEngine;
using UnityEngine.SceneManagement;
using UnityEngine.UI;
using System;
using System.Collections;
using System.Collections.Generic;

public class GameManager
{

	//Class Level Members Start


	//Class Level Members End


	//Method Start

    /// <summary>
    /// load all of the data on setup
    /// This should be called on the title screen
    /// </summary>
    public void Setup()
    {



    }


	//Method End

	//create a local instance of GameManager
    private static GameManager instance;

    //If there isn't a GameManager instance, create one.
    public static GameManager Instance
    {
        get
        {
            if (instance == null)
            {
                instance = new GameManager();
            }
            return instance;
        }
    }
	
    private void Shutdown()
    {
        if (instance != null) {
            instance = null;
        }	
    
    }

}