What potential pitfalls can arise when using session variables in PHP for storing shopping cart data?

Potential pitfalls when using session variables in PHP for storing shopping cart data include session data being lost if the user closes their browser or if the session expires. To solve this issue, you can serialize the shopping cart data before storing it in the session and unserialize it when retrieving it.

// Serialize the shopping cart data before storing it in the session
$_SESSION['cart'] = serialize($cart);

// Unserialize the shopping cart data when retrieving it from the session
$cart = unserialize($_SESSION['cart']);