How do I delete a single file from the Trash? I'm trying to free up space on an external drive, and after deleting a bunch of stuff, it's still showing very little actual free space.  I went to the trash can, but can't seem to delete the files there other than by emptying the entire trash.

Am I missing something?  What's the point of having a "staging area" for stuff you (probably) want to delete, if you can't get rid of the files in it individually?  The drive will be used on an embedded system, so just "putting files in the trash" doesn't actually make space on the drive, as far as the consuming device is concerned.
The Trash isn't intended for files you may want to delete later but rather as a safety net if you delete the wrong files. If you want to mark files for later deletion, either use a dedicated folder (as already mentioned in another comment) or mark them with a specific label/color.

To delete individual files from the Trash


Open the trash in the Finder
Open Terminal.app
Type rm -rf and then one space character at the end
Drag one or more files to be deleted into the Terminal window ('til you see the green + sign)
Press Enter in Terminal.app
Puff, files are gone!


If you need this very often, I would recommend writing a service using Automator or getting more familiar with Terminal.app/bash.