Halloween is fast-approaching, and there are only two things scarier than the costumes themselves: having the same costume as someone else, or, conversely, being totally not trendy. The National Retail Federation — a retail trade association — is generally acknowledged as the authority on the year's best-selling costumes, but what about the homemade costumes? Based on a variety of sources, we've researched the costumes you're most likely to see on Halloween. Plan accordingly!