Years ago, there was a ring of thieves in my area stealing gear from wedding photographers. Not only cases and bags, but gear left for just a few moments. One photographer had his camera rig stolen when he put it down by the cake table to go to the bathroom.
I had a case of gear stolen at a wedding reception. The thieves actually cut through the tripod bag handles to get to the gear, since I had cabled it up. My gear went from Northern California to Southern California in 2 weeks, and one of my cameras ended up on e-bay.
Insurance is a good idea, of course, but consider that if you file a large claim, you stand a good chance of being dropped, and you will have to find another carrier. Happened to my associate, whose $10,000 of Hasselblad lenses got stolen.
Moral of the story:
1. Never leave any gear lying around. Set up so that you can carry your active gear on you. Never put a bag of gear down where you do not have your eyes on it constantly. If you need to go to the bathroom, take your gear with you.
2. Get an alarmed cable lock. Use it. I use hard cases that can't be cut. Also, good locks. Realize the alarm will not be heard over loud dance music. I carry two cables, in case I want extra security.
3. Never trust venue personnel to do any watching for you, even in a 'protected' back room. Never rely on the DJ, bartender, or anyone else, such as an assistant or second shooter, unless the assistant's only task is to sit on your gear. The associate mentioned above set his bag by the DJ. The DJ also got his camera stolen. DJs and your assistants or second shooters have other things to do besides watch your gear, and thieves know it. And guests, even if they see your gear being stolen, have no idea it isn't your assistants lifting the gear. Guests saw the thieves that took my gear, but said nothing, of course.
4. If you have back up gear in the trunk of your car, secure it, and don't go in and out of the trunk unless absolutely necessary. People are watching.
5. Always put all memory cards in a case on your person--not in your bag. Before leaving for the day, take used memory cards out of the camera, in case you are robbed. Nothing--not even insurance--will get your wedding client's images back, once they are gone. I read about a photographer who had a secret pocket sewn into his pants leg for the memory cards.