What are potential pitfalls to avoid when using session variables in PHP for data storage?

One potential pitfall when using session variables in PHP for data storage is not properly sanitizing user input before storing it in a session variable. This can lead to security vulnerabilities such as cross-site scripting attacks. To avoid this, always sanitize user input before storing it in a session variable.

// Sanitize user input before storing it in a session variable
$_SESSION['username'] = filter_var($_POST['username'], FILTER_SANITIZE_STRING);