Like many enthusiasts, I have been on a ton of different coaster types, a bunch of times. I would conservatively estimate I have done 2,000 laps on coasters, and have lost stuff out of my pockets twice.
Once was in 2009 on Colossus @ MM. I was working so I had a collared T. I put some stuff in my shirt pocket, and lost it all on the first air time hill.
The second time was last Friday on Freedom Flyer at Fun Spot, The new Vekoma Junior seats at like a 70 degree angle, and everything slide right out of my pocket and fell the 20 feet to the concrete. My phone broke apart but the screen was not damaged and it still works!