I'm posting from the rec.crafts.metalworking newsgroup.
278) It looks to me like an iron-based meteorite, with the surface contours resulting from the heating as it fell through the air. 279) A custom wrench for some particular tool. It looks as though the handle end is intended to serve to lever something up. I think that the central open end is a bit larger than the hex. The notches to either side may be tiny open-end wrenches, or may be intended to bend something to adjust it. Is this another of the items from that typewriter repair kit? 280) A combination tool for a musician. It seems to be primarily an electronic metronome, with the ablity to select rhythms as well (perhaps a virtual drummer), and a source for an A=440 Hz tuning tone. 281) I think that is a fisherman's knife. The notch on the tip is for removing a fish hook from the fish's mouth. The notches on one side are for removing scales. 282) You say "extreme close-up", but you don't give the dimensions. It looks as though it has been bent or trimmed along one edge (at about 4:00 or so). Depending on scale, it could be a plate for the output end of a meat grinder, or perhaps the aperture plate for an aerator for a faucet. The holes are to the wrong scale for it to be the aperture place for a hose and shower for the bathroom. 283) This is a strange one. Looking only (or mostly) at the second photo it looks as though the spike on the end could be stabbed into a stuck lid or a jar of mayonnaise or the like, and then the handle rotated down to drive the second spike into it to get a good leverage for unscrewing the lid. But if so, I don't know what the feature at the other end of the handle might be.Now to see what others have answered.
Enjoy, DoN.