What are some best practices for handling session data in PHP to ensure successful data retrieval?

When handling session data in PHP, it is essential to ensure that the data is properly stored, retrieved, and managed to avoid any issues with data loss or corruption. One best practice is to always start the session before accessing or setting any session data using session_start(). Additionally, make sure to properly sanitize and validate any data being stored in the session to prevent security vulnerabilities. Lastly, always check if the session data exists before trying to retrieve it to avoid errors.

<?php
// Start the session
session_start();

// Store data in session
$_SESSION['user_id'] = 123;

// Retrieve data from session
if(isset($_SESSION['user_id'])) {
    $user_id = $_SESSION['user_id'];
    echo "User ID: " . $user_id;
} else {
    echo "Session data not found";
}
?>