Any mechanic, craftsman, or hack who works around metal/wood/plastic will instantly recognize the utility of the simple metal file. They don't/shouldn't cost a bunch of money and you don't need a huge set with a fancy pearl inlaid box. They do, however, need to have large & comfortable handles and be heavy enough that you can get your elbow into whatever you need to file. The ones pictured here is a 3-piece set of Craftsman 8-inch files that you can buy for $21.99 on Craftsman.com, but you could also pickup a 6-piece set of Woodstock metal files (includes some square and triangular pieces that can be handy for) for $20.63 via amazon.com and DT makes a few pennies if you buy those via our amazon affiliate program.
So, what do you use these little bastards for? Well, any time you need to remove a small amount of metal, wood, plastic, papier-mâché, or whatever from anything -- you can just whip out the file and hack away -- no special tools, training or safety measures needed...well...you should probably wear eye protection (and gloves if you are dealing with metal) but there are all kinds of videos on youtube showing you how to use your file if you can't figure it out.
What about you -- what is the forgotten hero of your toolbox?