Item 1: Definitely a horse-harness "buckle." The photo below shows a very similar one, as part of the horse's bridle, just above the horse's mouth.
2: Lock-cover from the frame of a mid-1800s carpetbag.
3: Civil war era New York State Militia officer's button, "coat size," (with most of its goldplating remaining).
4: US Army Enlisted-men's "general service" coatbutton, "coat size"... yours is the 1854-1874 version.
5: Same as item #3 except "cuff-size"... with no goldplating remaining on it.
6: Civil war era yankee soldier's kepi (hat) chinstrap-adjuster "buckle."
7: Various sizes of brass rivets from various leather equipment... used on everything from civilian (and military) horse-harness to soldier's equipment like cartridge-pouches, so there's no way to ID (or time-date) those with any certainty.
8: The small lead disc with what looks like a bit of rust-staining on the edges from iron wire going through the disc does look like one of the varieties of lead seals... such as a bale-seal or cloth-seal, etc. Used continuously from at least the early-1800s (and perhaps a bit earlier) through today. But if you dug it right among the civil war relics, it is probably from that era.
