Have you ever been in the situation where you have to check bags with some valuable equipment in them? Sometimes our gear exceeds carry-on limits, and we're forced in to this nerve-racking Plan B. For these moments, keep a handful of plastic security ties on hand.
I got this tip when I was on the TWiP show with Alex Lindsay, and he was describing how he handles trips with lots of photo equipment. Alex's advice was to make sure you have insurance for your gear, then use the plastic security ties on the bags that you have to check. They are actually a better deterrent than cheap locks, and once they have been cut, they can't be reattached -- letting you know right away that your bag has been opened.
No system is perfect under these circumstances. But I like Alex's idea, and I'm going to purchase a bag of security ties for my upcoming travels... just in case.