Pixie Dusting
On Disney Cruises, it's traditional to bring along a number of small gifts which you will 'pixie dust' to other kids and staterooms throughout the cruise.

Magnets 
Customized to your ship and year of sailing.  Magnets fully enclosed and not visible from the back.  $30 for 25, $50 for 50, $100 for 110

Fidget Clickers
Same design as magnets, but larger fidget clicker case and mechanical keyboard switch for a satisfying 'click' each time it's pressed.  Also includes a keychain attachment.  HUGE hit with kids.  
$3 for 1, $25 for 10, $55 for 25, $100 for 50, $200 for 110