My cheap bike computer fell off on my morning commute today. I was taking the lane in heavy traffic and the computer disappeared under a bus. I didn't bother to go back for it.

Before I found panniers and rear racks that worked well, I dropped a pannier with a laptop in it (three times!) This happened to two different laptops. Both initially survived, but one of them died later.

I've lost several blinkies, a couple of water bottles, a coffee cup, and once my chain. It broke and unspooled into the middle of a busy intersection. I didn't go back for it either. I had just bought a new one and had it with me.

What have you lost?