The first thing we need to do is to create a new C# script and name it Inventory. When you open the script, delete the Start and Update functions, leaving an empty class for us to use.

First, add this using statement where the other using statements are. The using statement will be needed so that we can use the List container variable:

using System.Collections.Generic;

Now, let's add the variables we require and place them after the opening class defining bracket:

bool showInventory = false;
public Rect inventoryRect = new Rect(Screen.width / 2, Screen.height / 2, 400, 400);
public GameObject EmptyObject;
public int InventorySize = 9;
public GameObject[] invItems;
public GameObject[] QuickItems;

List<KeyValuePair<int, GameObject>> items = new List<KeyValuePair<int, GameObject>>();

List<KeyValuePair<int...