Cheap USB flash sticks
As well as a couple of on-line backups of my data, for several years I've carried a LUKS encrypted 64GB USB flash stick around with me. New photos have caused the amount of data to grow, so I recently bought a 128GB drive. It encrypted OK, then formatted as ext4, and the rsync worked OK for a while, then it started throwing errors and became unusable.
I can only assume that recent cheap USB sticks concentrate the wear levelling of erase blocks in the areas used by the FAT, and having file metadata stored anywhere else, as any other filesystem format will do, will cause rapid damage.
A quick google later, I've just found this site: How to Damage a FLASH Storage Device which confirms my suspicions.