~/App_Code/Cart.cs

Add ASP.NET folder

protected void OnSomeButtonClicked(object sender, EventArgs e)
{
  if( someCondition )
  {
    Response.Redirect("~/Other.aspx?action=runAway");
  }
}

protected void Page_Load(object sender, EventArgs e)
{
  if( !IsPostBack )
  {
    if( "runAway".Equals(Request.QueryString["action"] )
    {
      RunAway();
    }
  }
}

protected Button1_Clicked(Sender s, Eventargs e){
        MyNamespace.Page_Other po = new MyNamespace.Page_Other();
        po.Method1();
        Response.Redirect("~/page_other.aspx");
}