When plugging a USB stick into a Mac, OS X creates a number of hidden files on the stick, including a Spotlight index and Trash folder.
Example from the terminal for a USB stick "Untitled":
$ ls -a /Volumes/Untitled .Spotlight-V100 .Trashes ._.Trashes .disk .fseventsd
It even does this on the xD memory card for my camera, so after having copied my pictures and deleted them from the card, the card is still full.
Is it possible to turn this off for USB and memory cards, so OS X either writes these files to the primary disk or doesn't write them at all?