I've been a victim of camera theft. I had a camera bag taken from an unlocked car in my driveway; it was a horrible feeling. I lost just about everything and it didn't matter that it was my fault, the fact remained that if you have your cameras stolen, it will pretty much ruin your day, your trip, or just maybe your livelihood.
Maybe it was that long ago feeling that still makes me incredibly nervous, sometimes to the point of anxiety, when I have to leave camera equipment in my car, that had me searching for the best solution to keep it safe.
And minimizing the ability of someone to relieve you of your gear, whether it's in your car, on a train or back at the hotel, will give you the peace of mind to concentrate on taking great photographs or enjoying a meal during down time.
Even if you plan on carrying all your cameras and lenses on your person, you certainly aren't going to carry your laptop, hard drives, and other peripherals.
So what can you do to decrease the likelihood of theft? Decrease, because nothing will stop a determined thief, especially if they have time.
1. Many camera bags or equipment cases can be locked, so take advantage of that. I use a Thinktank roller bag which has a cable that allows me to secure the bag to an immovable object, like a tie down point in my car.
2. For camera bags that do not have built-in locks, I've found the PacSafe Backpack and Bag Protector to be the perfect solution. Realize that a thief can still reach zippers through the mesh, so I use an additional lock on the compartment where I keep items that could be removed, such as keys, a hard drive, flashlight, etc. The PacSafe also has a cable that can be secured to a fixed object.
Final advice is to be aware of your surroundings. If you are at a location known for photography, it pretty much is a given that you have gear in your car. And while you could bring less gear and travel lighter, you've invested in it and after all the effort to get to the best location, you don't want to be without it.
Video demonstration of the PacSafe.