public static PersistentManagerScript Instance { get; private set; }

public string Value;

private void Awake()
{
    if (Instance == null) {
        Instance = this;
        DontDestroyOnLoad (gameObject);
    }
    else
    {
        Destroy (gameObject);
    }
}

// Use this for initialization
void Start () {

    Value = "camilo";

}

// Update is called once per frame
void Update () {

}

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;
using UnityEngine.SceneManagement;

public class SceneManagerScript : MonoBehaviour {

public Text ValueTxt;

private void Start()
{
    ValueTxt.text = PersistentManagerScript.Instance.Value.ToString ();
}

public void GoToCategories()
{
    SceneManager.LoadScene ("Categories");
    PersistentManagerScript.Instance.Value;
}

public void GoToSubCategories()
{
    SceneManager.LoadScene("subcategories");
    PersistentManagerScript.Instance.Value;
}