Mangum, the brass rivet is for holding two thick pieces of leather together. Most seem to have been used on horseharness leather, but could be from many other leather items such as saddlebags, pouches, suitcases, and belts.
The small brass object with a circulat flat disc and a narrow rectangular slot on its other side resembles a rivet, but isn't that. Seen 'em before but can't recall what it is.
I agree with Old Digger, the Smith Durham object is a bibb overalls snap or rivet-button. I also agree with him that the object in photos 9 through 12 is a faucet-handle.
I agree with Kuger, object on the left in photos 2 & 3 is a sideplate from a padlock.
I agree with Creskol about the object in photos 6 though 8, except for a slight difference in its name. It is shown in an 1895 Sears & Roebuck mail-order catalog as a "Whiffletree Tip." It had a slot for a leather strap on its smaller end, but the slot on yours has been bashed-down closed. See the catalog scan, below. A photo shows an undamaged dug one, and another photo shows a modern one in use on a buggy's whiffletree/singletree.
