I hit a bump while crossing a 4 lane highway, and watched my big Cateye blinkie bounce off, just as the light changed. It was crushed under the wheels of a truck.

My prescription glasses fell out of my pocket. I was wearing sunglasses at the time and didn't even notice. I went back to where I thought they would be. Sure enuff they were there. Flatter than a pancake! Good thing I had a spare.

So far I've only lost two relatively cheap taillights. One of them twice this week - I retrieved it the first time, a little worse for the wear. When it started disintegrating in situ yesterday, I just let it happen. Wasn't worth stopping and going back to pick up the pieces.
It's diabolical how those clip-on taillights can dislodge themselves from a cargo trunk loop while riding - they take a concerted effort to remove by hand!
My route has some rough railway crossings and potholes that I'd rather not slow down for, so it is a bit of a challenge for non-permanently mounted hardware.
I'm going to start adding permanently mounted rear reflectors to all my bikes, so at least I have some protection if the taillight comes off.

Just two days ago I lost my rear light in traffic. Didn't bother getting it back.

Twice I've had a pannier fall off (one a over pothole and the other while hopping a curb). Luckily it wasn't in traffic and the contents were undamaged.

Over the years I've had the following fall off (or dropped) from my bike while riding: a few lights, a few reflectors (usually the ones on pedals), a sports watch (I had attached to my handle bars), a couple water bottles, and a pannier bungee cord bracket.

I've also jettisoned a pannier, complete with notebook PC (company owned). If there was any damage done to the PC, it was latent, as it continued to function for a couple years more before it needed to be put out to pasture.

I'm a big believer in electrical tape, zipties and rubber straps so I only drop something out of a jacket pocket. A phone once or twice.

I did that once, hit a deep pothole, pannier w/ work laptop flew off right in front of a bus but it rolled to the side so the computer survived. Whew. Those panniers I have since relegated. My 10 yr old still uses them to carry board games or nerf weapons over to friends' houses.

I have dropped taillights several times. Sometimes from the mount, other times they just pop open and spew batteries all over the place too.

I've resumed riding my bike that has a computer lately and twice in the last week when I park it in the garage at home the computer is twisted in its mount. Not sure when that's happening, if it's moving the back past my kids' into the garage, or during the agony of climbing the last hill.

Never dropped anything quite the way you guys have. Anything I've ever lost off of my bike was either a direct result of an accident or theft.

Now I see what keeps the LBS in business. It's the accessories!

A headlight fell off once (poor strap mount) but got caught in the brake and gear cables so I didn't lose it

Lost some nice sunglasses out of my pocket (should have zipped the pocket - duh!) and turned around to watch a bus run over them!

Apart from that I've been pretty lucky. My dinotte light is quite secure in the rear, I have a screw on dynamo light, and lock blocks for headlights.

Daven

My water bottles used to escape frequently until I started putting them into the neoprene can koozies.

Blinkies seem to fall off the saddlebag loop more than they should. Also lost one I had installed on the rear rack pannier frame. I consider the cheap blinkies a disposable item and try to ride with more than one. The small one on the back of my helmet is my backup. I will also clip an extra blinkie to a jersey pocket if I have concerns about a battery running down mid-ride. Some of my friends have zip-tied their blinkies to their saddle bag, then just replace the zip-tie when it's time to change the batteries. That also helps with the blinkies rattling themselves apart.

The only thing I've ever lost off the bike was....the two bottom bolts of my rack due to my own inattentiveness to appropriate routine maintenance. That led to an "OMFG card-in-the-spokes on steroids" moment at 25mph on a downhill when the bracket got into the cassette.

Fortunately, the bracket contacted the cassette ahead of the rotation rather than behind; the alternative might have been....eventful. They must have gone nearly simultaneously. Otherwise, the one loose bracket would have alerted me with its' rattle against the boss.

I've lost a bicycle lock cable and a couple of blinks. However, I've found a lot of things along the road that I brought home so feel like I'm in the black.

oh yeah, I lost the bolt holding my downtube shift lever on. at the beginning of one commute (shifting got real sloppy on the way in, but didn't bother investigating it and then on the first or second shift on the way home the lever fell off and was dangling by the cable. Since it was my right lever and I ride a triple, I rode home on a 3 speed.

Couple of years ago I was leaving a rest area on the local rail trail as two 14-15 year old bmx'ers pulled in. Just started to pedal when I hear this "Hey you, come back." I at first thought they were mocking me or wanted to cause trouble, but I looked back and see this kid come running up to me with something in his hand....MY WALLET. Fell out some how and as the kid was standing there, I opened it to check the cash (had over $100) and kid says, "It's all there mister." I said, "I know it is, except for this," and handed him a twenty. Thanked him again and rode off feeling good about my fellow man and upset for being so stupid for almost losing my wallet.

My daughter had this problem with her Sigma. I put a very thin strip of tape around the circular part on the back of the computer that twists into the mount. It creates a firmer connection, and you can't see it. Hasn't fallen off again (yet). Granted she's only ridden a few hundred miles since I put the tape on. I imagine if you take your computer off a lot you might have to replace the tape often.

So far just a rear blinky has fallen off, but I did miss the bottle cage once after I took a drink and my water bottle went rolling down the street.

I lost a high tech car key from a pocket of my front bag. Over $500 to replace - OUCH!!

Mostly rear blinkies. Not cheap ones, either.

Ah, you reminded me of something which means I fudged a little when I said nothing falls off. I found a really nice blinkie on the road, clipped it on my rear rack and used it for about a week before it fell off. Basic reasoning should have informed me that it was prone to falling off

I tend to go my own way on these things. Just a strip of tape around the computer's mount, and tape or zipties on blinkies and they never fall off. My patch/tool kit is strapped on with inner tube rubber and velcro fasteners. It isn't pretty but it's out of the way and won't fall off.

The one I lost Friday was a Strada also. I liked the computer, other than the mount. I ordered a Sigma as a replacement, as I have several and they've never fallen off.

I on the other hand, had lots of issues with a wireless sigma one (interference giving weird readings, no readings, stopped working randomly). Maybe I'll just use electrical tape (black so not as noticeable, stick it there, but removable when I want to change batteries) to stick it more permanently to the mount and stop taking it in with me when I stop anywhere - because who's really going to steal the head unit to a $30 computer.

I accidentally left the lid of my trunk bag unzipped one morning, and less than a mile from home I jumped a curb and my heavy lock & chain ejected into the mud. Fortunately nothing else escaped, but I had to rearrange the bag's other contents to keep them from getting filthy.

Cateye Strada wireless came off once. Heard it... wasn't sure what it was... found out what I lost about mile and half later. Loop back, grabbed it on the bike path, rushed to train barely to make it in time.
Dropping on to me on the other hand most recently was 2 inch thick tree branch on my head... glad my helmet covered me nicely. I was wondering what were the chances of that happening as well as it landing on my helmet not on my back, hand, etc... (Road bike so I stretch out quite a bit)

None of mine are wireless. Wired computers are simpler, nearly always work, and have longer battery life.

Yeah, that's why I switched to wired on my current one. Guess the first one was on a really good sale for a reason.