LOST.DIR and .Trash-1000 you can delete the contents of all the folders...freed up 5GB on my card by doing just that...the other stuff can't say for sure as they are most probably from apps you have installed...
If its on your SD card you can save your pictures on a computer, or the entire contents of the SD card for that matter, then format the entire card. Make sure you move all your apps back to the phone first so you don't lose anything. Then you'll have a practically new card. I've done it twice.