Wallet, passport, tickets and keys zipped (or velcro'ed) up in your crashpad, travel light in bouldering areas and move your stuff around with you (or leave it next to the recovering hungover/ injured / lazy person in your group).
If you have a car full of stuff and it's the weekend either go somewhere busy where there are likely to be people (not thieving types) around coming and going all day ie. Apremont, Sabots, Cuvier.. Or go somewhere really off the beaten track that thieves aren't likely to know about. Whilst the busier spots will be perfectly safe in the day time, don't stay at the crag too late, you may return to an empty car park and a smashed window, there maybe people waiting around later in the day for an opportunity or more likely a crew that scans round all the main carparks looking for an opportunity.