Populate inventory with item icons

Hello everyone. I have my inventory window setup the way I want, but right now it only displays the number of the slot. I’ve been using a mish mash of tutorials that explain how to populate the inventory with random items from chests etc but I have a set number of items I need to place in the inventory. How can I get the item icons to show up in the slots?

using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class MyGUI : MonoBehaviour {
	public GUISkin mySkin;

	public  float lootWindowHeight;
	
	public float buttonWidth = 40;
	public float buttonHeight = 40;
	private float _offset = 10;
	
	/********************************************************/
	/* Inventory Window Variables*/
	/********************************************************/
	private bool _displayInventory = true;
	private const int INVENTORY_WINDOW_ID = 1;
	private Rect _inventoryWindowRect= new Rect(10,10,170,265);
	private int _inventoryRows = 6;
	private int _inventoryCols = 4;
	private const string ARMY_MEN_PATH = "Item Icons/Army Men"; 
	// Use this for initialization
	
	void Start () {
		
	}
	
	// Update is called once per frame
	void Update () {
	
	}
	
	void OnGUI(){
		_inventoryWindowRect = GUI.Window(INVENTORY_WINDOW_ID, _inventoryWindowRect,InventoryWindow, "Inventory");
	}

	public void InventoryWindow(int id){
		int cnt = 0;
		for(int y = 0;y < _inventoryRows;y++){
			for(int x = 0;x < _inventoryCols;x++){
				GUI.Button(new Rect(5 + (x * buttonWidth),20 + (y * buttonHeight),buttonWidth, buttonHeight),(x + y * _inventoryCols).ToString());
				GUI.Button(new Rect(5 + (x * buttonWidth),20 + (y * buttonHeight),buttonWidth, buttonHeight),(x + y * _inventoryCols).ToString(),"box");	
				cnt++;
			}
		}
		GUI.DragWindow();	
	}
	
	public void ToggleInventory(){
		
	}

}

Hopefully helps!