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.