My rear view mirror fell off of my commuter several years ago. In retrospect, it had been getting loose for a while & I never adjusted it. I was able to retrieve it.

the only other thing I lost was my old, crappy headlight right before a very steep descent on an unlit road in the dark. The light was an old Specialized one that ran on 4 AA battereis & the top of the casing flew off, then the batteries & the lamp flew out (since they were now unsecured). I spent a good 5 minutes looking for parts int he dark. I found most oft he parts, but many were broken. I usually go 40 down that hill, but I must have gone like 5 miles an hour the entire way after losing the light.