`UnityEngine.GameObject' does not contain a definition for `text' and no extension method `text' of type `UnityEngine.GameObject' could be found (are you missing a using directive or an assembly reference?)

Trying to find all Text tagged as “Item01” and set its text to Item01’s Text.
using UnityEngine;
using System.Collections;
using UnityEngine.UI;

public class DisplayItemCount : MonoBehaviour {


	public Text Item001;
	public Text Item002;
	public Text Item003;
	public Text Item004;
	public Text Item005;
	public Text Item006;
	public Text Item007;
	public Text Item008;
	public Text Item009;
	public Text Item010;

	public GameObject[] Item001_B;
	public GameObject[] Item002_B;
	public GameObject[] Item003_B;
	public GameObject[] Item004_B;
	public GameObject[] Item005_B;
	public GameObject[] Item006_B;
	public GameObject[] Item007_B;
	public GameObject[] Item008_B;
	public GameObject[] Item009_B;
	public GameObject[] Item010_B;


	// Use this for initialization
	void ItemDisplay () {

		Item001_B = GameObject.FindGameObjectsWithTag ("Item01");
		foreach (GameObject Item01 in Item001_B) {
			this.gameObject.text = Item001.text; // assign text to text
		}
	}


}

GameObjects don’t have a .text field, only a text component attached to the game object has the .text field.

So you need something like this:

foreach (GameObject Item01 in Item001_B)
{
    Item01.GetComponent<Text>().text = Item001.text; // assign text to text
}

Also FindGameObjectsWithTag is very slow, you really should store references to you text elements so you can look them up without doing a find.