The apron, the jeweler's bench, the sheet, are all good ideas, but the really hard part, when something has fallen on the floor, is not stepping on it or rolling it over, if you have an office chair. When something hits the floor, the first thing I do is freeze.
And sometimes, it's not the small stuff, but the larger pieces. I have a rattail file, about four inches long, that launched itself into space. It's in the basement, within a six-foot area behind my seat at the bench, and I'll be darned but I haven't found it yet.
Someone else mentioned the gray painted cement, and that makes me think of a variation on the sheet idea-if your bench is on a slab, paint the slab white under the floor.
Regards,
Brad