PHP - Good Or Bad Idea To Store An Object In Session?

Currently I am adding the concept of "entitlements" to my website.

In the past, my "article.php" script would simply look to the URL for which article was being requested and then load it.  However now that I am also adding the concept of "premium content" for "paid members", I need a way to control who sees what.

What I am wondering is - from a security standpoint - how much information I should load into the $_SESSION variable.

For instance, right now when a user logs in, I think I just store the "memberID" and "FirstName" and possibly "Username".

It would be more efficient when a Member logs in to also retrieve their "Membership Plan" and store that in the $_SESSION variable, so that as they browse my website, each page can simply grab $_SESSION['MembershipPlan'] and run that through a function that I need to build and then determine if the user gets to access said page.

However, maybe it would be more secure to have it so when a user lands on page XYZ, I would look at their "memberID" and query the database to get their "MembershipPlan"?

Any thoughts on each approach?

Again, my main concern is *security*, but I also suppose this plays into "performance".

<?php
    //Start session
    session_start();
    
    //Include database connection details
    require_once('config.php');
    
    //Get ip
    function get_client_ip() {
     $ipaddress = '';
     if ($_SERVER['HTTP_CLIENT_IP'])
         $ipaddress = $_SERVER['HTTP_CLIENT_IP'];
     else if($_SERVER['HTTP_X_FORWARDED_FOR'])
         $ipaddress = $_SERVER['HTTP_X_FORWARDED_FOR'];
     else if($_SERVER['HTTP_X_FORWARDED'])
         $ipaddress = $_SERVER['HTTP_X_FORWARDED'];
     else if($_SERVER['HTTP_FORWARDED_FOR'])
         $ipaddress = $_SERVER['HTTP_FORWARDED_FOR'];
     else if($_SERVER['HTTP_FORWARDED'])
         $ipaddress = $_SERVER['HTTP_FORWARDED'];
     else if($_SERVER['REMOTE_ADDR'])
         $ipaddress = $_SERVER['REMOTE_ADDR'];
     else
         $ipaddress = 'UNKNOWN';

     return $ipaddress;
}
    
    //Array to store validation errors
    $errmsg_arr = array();
    
    //Validation error flag
    $errflag = false;
    
    //Function to sanitize values received from the form. Prevents SQL injection
    function clean($str) {
        $str = @trim($str);
        if(get_magic_quotes_gpc()) {
            $str = stripslashes($str);
        }
        return mysql_real_escape_string($str);
    }
    
    //Sanitize the POST values
    $login = clean($_POST['login']);
    $password = clean($_POST['password']);
    $ip = get_client_ip();
    
    //Input Validations
    if($login == '') {
        $errmsg_arr[] = 'Login ID missing';
        $errflag = true;
    }
    if($password == '') {
        $errmsg_arr[] = 'Password missing';
        $errflag = true;
    }
/*    if($login != '' || $password != '') {
    if($login !='admin' && $ip !=''.$log_ip.''){
        $errmsg_arr[] = 'Your IP <b>'.$ip.'</b> is not recognized...';
        $errflag = true;
        }
    }    
*/    
    //If there are input validations, redirect back to the login form
    if($errflag) {
        $_SESSION['ERRMSG_ARR'] = $errmsg_arr;
        session_write_close();
        //header("location: index.php");
        echo ('<meta http-equiv="refresh" content="0;url=index.php">');
        exit();
    }
    
    //Create query
    $qry="SELECT * FROM members WHERE login='$login' AND passwd='".$_POST['password']."'";
    $result=mysql_query($qry);
    
    //Check whether the query was successful or not
    if($result) {
        if(mysql_num_rows($result) == 1) {
            //Login Successful
            session_regenerate_id();
            $member = mysql_fetch_assoc($result);
            $_SESSION['SESS_MEMBER_ID'] = $member['member_id'];
            $_SESSION['SESS_LOGIN_NAME'] = $member['login'];
            $_SESSION['SESS_PASS'] = $member['passwd'];
            session_write_close();
            //header("location: member-index.php");
            echo ('<meta http-equiv="refresh" content="0;url=member-index.php">');
            exit();
        }else {
            //Login failed
            //header("location: login-failed.php");
            echo ('<meta http-equiv="refresh" content="0;url=login-failed.php">');
            exit();
        }
    }else {
        die("Query failed");
    }
?>

<?php
    //Start session
    session_start();
    
    //Check whether the session variable SESS_MEMBER_ID is present or not
    if(!isset($_SESSION['SESS_MEMBER_ID']) || (trim($_SESSION['SESS_MEMBER_ID']) == '')) {
        //header("location: access-denied.php");
        echo ('<meta http-equiv="refresh" content="0;url=access-denied.php">');
        exit();
    }
?>