Way back in 2005—you know, the old days—I wrote about a few ways to work with files in the trash. The main reason I typically want to “work with” a file in the trash is to confirm that, yes, this is in fact the file I meant to throw away. So really, opening the file with an application, as suggested in the prior hint, is a fair bit of work given I just want to glance at the file before emptying the trash.
As of OS X 10.5, though, there’s a much simpler solution: you can use Quick Look on files in the trash. So when you’re not sure whether a file is really the one you wanted to trash, just click once to select it in the Finder, then press the Space Bar. Assuming the file is from an application that creates Quick Look previews, you can then easily make sure it’s the file you meant to throw away. If the file doesn’t have a Quick Look preview, of course, you’ll have to resort to one of the methods in the previous hint to check its contents before emptying the trash.