Yours is a modern 'Ring Thing' as Dad & I call it. These thin copper types are 20th C. (I think some kind of internals for an engine or other mechanical thing). You will find some thicker bronze versions (same size) which are Medieval Horse Harness Rings, & some older versions that are Roman. Lots of debate on the function of them & I'm sure that they had many.
No idea on the little finial shaped piece. (Pawn like)
Pistol Shot (Lead ball)
The interesting broken buckle, I'm struggling to date. Pretty sure its an 18th C Shoe Buckle bit, but it maybe a very early circa 1720 type.