A member of seabreeze.com.au "FlyingWhiteBoy" compiled this info after his "years of mentoring juvenile offenders."

NEVER EVER EVER leave anything in your car that could remotely be seen as stealable. All popular kite/wind/surfing spots are on the circle route of carparks that thieves drop by multiple times every day. If you leave a handbag on a car seat, more times than not you will loose it at a place like Woodmans Point or Leighton (WA). Note that local cars are not safe, they dont care where you live.

How to minimise the risk of a broken car window+stolen gear
- Leave your mobile phone and wallet at home, they are never safe on the beach or in your car.

- Never leave any type of bag in your car, they will smash your window to check whats inside.

- Never leave sheets, towels etc looking like they might be covering something. I know a friend who lost a digital camera wrapped up in a beanie stuffed into the corner of his car boot.

- Leave all glove boxes and consoles open to show there is nothing in there. On days where car thieves have not pulled much of a loot they get desperate and will smash your window to check your glove box.

- Do not leave clothes hanging in the car, it shows your are going out somewhere afterwards or have just been out somewhere and thus you have a wallet and mobile in the car or on the beach.

Read more in the forums...

- Any sign of a stereo with a face that could have been left in the car is justification for smashing your window. If you pull into the car park with your music blaring, you don't know who is listening. They know that you don't take your stereo face onto the water.

- A radar detector left in a car will get your window smashed.

Sometimes there is almost nothing you can do...
  There are places and situations where EVERY car will have its window smashed and its contents gone through. I've seen upwards of 20 successive cars with their windows smashed at some concerts, beaches, dinner parties, parking lots... with no regard to make/model or contents. Some people avoid this risk by driving a crappy car and leaving the windows down.

Fists of justice
   Do not attempt to physically apprehend these guys unless you are willing to break your board on their head or you have a baseball bat or you are chuck norris, they ALL carry knives and wont hesitate to make a nice hole in you.

Leaving stuff on the beach
  Leaving valuables in shoes or buried under clothes on the beach is like making a non tax-deductible donation to the people who make a living on other peoples misery. There is also a large risk of losing your car when you leave your car keys in a bag on the beach, not to mention what they will do when they have your address from your wallet and your house keys attached. Carry your car key on you while kiting (in a mini dry bag if it has an immobiliser built in). Leave your house keys at home.

A lucrative business...
  A good afternoon/evening of breaking into cars will net a talented young thief (who has the right connections) thousands of dollars - including selling stolen credit cards, bankcards (which can be used over the teller without pins at some banks), ids, mobiles, mp3 players, stereos, radar detectors, clothes, tools, sports gear, laptops, video and digital cameras, car rims (one kid i mentored had a $5000 set of car rims buried in his backyard), pda's... not to mention when they later visit your home with your house keys and steal your motorcycle, plasma screen, dvd player, stereo, computer, passport... It is highly lucrative and the risk is low especially if they are under 18 as the police can't hold them for long and their record is cleared when they become an adult. The only thing that will deter them is the belief that you have nothing worth stealing

Car theft
  Most of the thieves are not there to steal cars as they cannot easily make money from it, they are mainly after non trace-able goods, cash and cards. They do however usually go from carpark to carpark up and down the coast in stolen cars so they must pick one up from somewhere, plus a favourite past sport of some thieves is thrashing the buggery out of stolen vehicles then lighting them on fire.

Disable your car mechanically if you are worried about theft (disconnect spark plugs, battery, ignition wires, fuel line valves... the less obvious the better and preferably do it from inside the car so they do not watch you doing stuff under your bonnet). Thieves are not renown for their auto-mechanic abilities. Once again, do not leave your keys on the beach with your gear.

Windows down? Doors unlocked?
  I did not recommend leaving windows down and removing all valuables because I do know of a number of cases where frustrated thieves slashed up the car seats when there was nothing to steal (now that is truly a scumbag thing to do). But my dearest mother was one of 15 cars broken into outside a house party, her car was the only car without a window smashed because she left it unlocked... you would have to weigh it up - risk of vandalism -vs- risk of smashed window.

Insurance?
Most insurance companies say that not locking the car would void their cover. This would be in relation to contents theft, vandalism AND car theft. Simple and illegal way of getting around this is to smash the window if you do lose something expensive enough or if the vandalism is bad enough.

If you're worried about losing your kites out of your car when at the beach, look into getting them covered as part of your home/contents insurance. My policy has nominated items (kites, board etc) which are covered, even if they're stolen off the beach. Wasn't a big hike in premium for this option.