Nothing of any value, like towels? Well, a number of years ago, it was raining one morning so we decided to go up Pic Paradis because we had never done that. Just in case, we took our towels with us, since it usually doesn't rain for very long. They were in the "locked" trunk. When we got to the top, we parked the car and walked away a short distance to get a better view. There were also a few coins sitting in a cup holder in the console between the two front seats. When we returned to the car--maybe four or five minutes later--the coins were gone and one of the towels, too. Yes, just one of the two towels. Stealing is a way of life for some people and it almost doesn't matter how much or little they steal.
The late psychiatrist, Dr. Bruno Bettelheim, was once asked by a reporter why there is so much crime. He answered "because they like to do it." He was right, I believe. That's their job--thievery.
The OP was lucky, but I think the location played a role, too. Too many people coming and going there. We usually stop at Market Garden on our way in from the airport. But, even with all the people coming and going, we never leave the car unattended.