Use nylon cable ties on luggage
Sorry to hear about the disappearing wallet -- Yikes!
I always use a small colored plastic cable tie in place of a padlock on any checked luggage - upon pickup, I know immediately if the bag was opened and can check contents before leaving the airport. The ties are sold at any hardware store or Radio Shack for pennies and they can be cut open at your destination with a legal to carry nail clipper. Of course, the best solution is always never to check anything you can't replace, but know that's not always possible.