CollectGameItem.cs

using UnityEngine;
using UnityEngine.UI;
using System.Collections;

public class CollectGameItem : MonoBehaviour {
	public GameObject button;
	public int id;
	// Use this for initialization
	void Start () {
	}
	
	// Update is called once per frame
	void Update () {
	
	}
	public void TakeGameItem(){
		//button.transform.SetParent(panel.transform);
		GameItemsStorer.AddUncountableItem(id);
	} 
}

GameConfigurationStorer.cs

using UnityEngine;
using System.Linq;
using System.IO;
using System.Collections;

public class GameConfigurationStorer{

	const string FILENAME = "config";
	static float seLevel = 0;
	static float soundLevel = 0;
	static int speedChoose = 0;

	static public float SELevel{
		get{
			return seLevel;
		}
		set{
			seLevel = value;
		}
	}
	static public int SpeedChoose{
		get{
			return speedChoose;
		}
		set{
			speedChoose = value;
		}
	}
	static public float SoundLevel{
		get{
			return soundLevel;
		}
		set{
			soundLevel=value;
		}
	}

	static public void ReadFromFile(){

		string fullPath = Application.persistentDataPath+"/"+FILENAME;

		if(!File.Exists(fullPath))
		{
			WriteConfiguration();
		}
		else{

			var dataArray = File.ReadAllLines(fullPath);

			seLevel = float.Parse(dataArray[0]);
			soundLevel = float.Parse( dataArray[1]);
			speedChoose = int.Parse( dataArray[2]);
		}
	}
	static public void WriteFromFile(){

		string fullPath = Application.persistentDataPath+"/"+FILENAME;

		using(FileStream fs = new FileStream(fullPath,FileMode.Create,FileAccess.Write)){

			using(StreamWriter stream = new StreamWriter(fs)){

				string fullContent = 
					string.Format("{0}\n{1}\n{2}",seLevel,soundLevel,speedChoose);

				stream.Write(fullContent);
			}
		}
	}

}

GameItemsStorer.cs

using UnityEngine;
using System.Collections;
using System.Collections.Generic;
using System.IO;
using System.Linq;
public class GameItemsStorer {

	static List<int> uncountableGameItems = new List<int>();
	static int countableGameItem = 0;
	const string FILENAME = "gameitem";
	
	public static int CountableGameItem{
		get	{
			return countableGameItem;
		}
	}

	static public void ReadFromFile(){

		string fullPath = Application.persistentDataPath+"/"+FILENAME;
		if(!File.Exists(fullPath))
		{
			uncountableGameItems.Add(-1);
			WriteToFile();
		}
		else{

			var readItems = File.ReadAllLines(fullPath);

				var readUncountableItem
					= (from element in readItems[0].Split()
						select int.Parse(element));

				uncountableGameItems = readUncountableItem.ToList();
				countableGameItem = int.Parse(readItems[1]);
		}
	}
	static public void WriteToFile(){

		string fullPath = Application.persistentDataPath+"/"+FILENAME;

		using(FileStream fs = new FileStream(fullPath,FileMode.Create,FileAccess.Write)){

			using(StreamWriter stream = new StreamWriter(fs)){

				var listContent = 
					uncountableGameItems.Distinct().Select(e => e.ToString());

				string content = string.Join(" ",listContent.ToArray());
				stream.WriteLine(content);
				stream.WriteLine(countableGameItem.ToString());
			}
		}
	}

	static public void AddUncountableItem(int i){
		uncountableGameItems.Add(i);
	}

	static public bool IsUncountableGameItemExist(int i){
		return uncountableGameItems.Exists(e => e == i);
	}

	static public void RemoveUncountableItem(int i){
		uncountableGameItems.RemoveAll(e => e == i);
	} 
	static public void PrintGameItem(){

		var listContent = uncountableGameItems.Select(e => e.ToString());

		string content = string.Join(" ",listContent.ToArray());

		Debug.Log("List GameItem:"+content);
		Debug.Log("Countable GameItem:"+countableGameItem.ToString());
    }

	static public void AddCountableItem(){
		countableGameItem++;
	}

	static public bool IsCountableGameItemExist(){
		return countableGameItem != 0;
	}

	static public void RemoveCountableItem(){

		if(IsCountableGameItemExist()){

			countableGameItem--;
		}

	}

}

SceneManager.cs

using UnityEngine;
using UnityEngineInternal;
using System.Collections;

public class SceneManager: MonoBehaviour {
	// Use this for initialization
	void Start () {

	}
	
	// Update is called once per frame
	void Update () {
	
	}
	public void GotoScene(string sceneName){
		Application.LoadLevel(sceneName);
	}
}