How to stop OS X from writing Spotlight and Trash files to memory cards and USB sticks?
For just a particular mounted volume - like a flash drive called yourUSBstick in this example - these commands will remove existing cruft, stop Spotlight indexing now and in the future, stop the related fsevents logging, and disable the Trash feature.

mdutil -i off /Volumes/yourUSBstick
cd /Volumes/yourUSBstick
rm -rf .{,_.}{fseventsd,Spotlight-V*,Trashes}
mkdir .fseventsd
touch .fseventsd/no_log .metadata_never_index .Trashes
cd -


Other unfamiliar stuff you may still see you probably want to keep, like Apple double "._*" files and other Apple DS cruft relating to icons and window placement.