This actually happened over a year ago but I saved it as a reminder. As I was getting out of a 4x4 pickup truck my 70-300mm zoom lens fell out of my camera bag. Of course it fell the four feet to the pavement below and hit with such a nasty sound. To make it worse, it then rolled under the vehicle parked next to the truck stopping dead center under that vehicle. I only said one word when this happened - Sh**.
As I crawled on the ground and reached under the vehicle to retrieve my lens, my heart was crushed thinking I just busted my lens. Upon holding it, I heard the "chink chink" sound of broken glass. I didn't want to find out what that meant but I had to. I sat back in the truck and tried to remove the lens cap. I couldn't budge it. After some thought, I decided to unscrew the filter from the lens. The relief when I saw that the filter broke and the lens cap was bent but the lens seemed fine. Hours later I had calmed down enough to take an image with the lens and it was fine. I was lucky.

Lessons learned: always make sure your gear is secure before moving around and always use a protective filter on your lens.