PayPal Express order description: Attendee name + Event name. This also works for any other EE gateway that uses the formatOrderDescription method, including SagePay.

PayPal_example.php

<?php
//* Please do NOT include the opening php tag, except of course if you're starting with a blank file

add_filter( 'FHEE__EE_Gateway___order_description', 
  'att_name_event_name_order_description', 10, 3 
);
function att_name_event_name_order_description( $desc, $gateway, $payment ) {
  $desc = 'Tickets';
  $transaction = $payment->transaction();
  if( $transaction instanceof EEI_Transaction ) {
    $primary_registrant = $transaction->primary_registration();
    if( $primary_registrant instanceof EE_Registration ) {
      $attendee = $primary_registrant->attendee();
      if ($attendee instanceof EE_Attendee) {
        $desc = $attendee->get('ATT_full_name'); 
      }
      $event = $primary_registrant->event_obj();
      if ( $event instanceof EEI_Event ) {
        $desc .= '  ' . $event->name(); 
      }
    }
  }
  return $desc;
}