I'm with the majority: Yard sale items need prices. For clothing, which isn't likely to sell well anyway, it's a good idea to do the "fill a bag" thing.
Keep in mind what a yard sale is and isn't: You have a yard sale because you want to clear stuff out of your house, and you want to recoup a small portion of what you paid for it. No one really "makes money" on a yard sale -- not unless they got the stuff for free in the first place.
On the other hand, if you have things that are really valuable and you want to sell, you can sell for a higher price through ebay (or similar venues). Of course, this takes more effort on your part.
If you have "just stuff" and want to make the most money, box it up and donate it to charity . . . then take the write-off on your taxes. Of course, this assumes that you itemize.