Relicsguy, welcome to T-Net's "What Is It?" forum, the best place on the internet to get unknown objects identified CORRECTLY. Speaking frankly... most other places (though fortunately not quite all) are full of wild guesses from people who are sure they are correct, but they are wrong.)
Please add your location to your T-Net member-profile. It can be very important to know where a mystery relic was dug when we try to determine its correct ID.
Your first bullet is still too dirty for certainty in identifying it. As my friend Fyrffytr1 guessed, it might be a (yankee) Starr Carbine bullet. But it seems to have a wide groove above its base, which would make it a (yankee) Smith Carbine bullet. See the photos below.
As he also indicated, buying a $20 digital caliper is essential if you want to figure out the correct ID of the bullets (and coins) you find. A Starr Carbine is .54-caliber, and its unfired bullet typically measures about .552-inch. A Smith Carbine is .50-caliber, and its bullet is typically about .524-inch. Thus, you see how important the caliper is, to detect the .03-inch difference between those similar-looking bullets.
Your second bullet is a "generic" 3-groove Minie-bullet which has been fired. The fact that its base- cavity is off-center is often (but not always) an indication of Confederate manufacture. Is the base cavity's shape a pointed cone, or a parabola, or something else?
The third bullet is a (strictly CS-made) Gardner's Patent Minie-bullet, which is in unfired condition. It appears to be the .58-caliber version, but precise measurement with the caliper is needed for confirmation.
I agree with Smokey... the round flat brass object is a grommet, most likely from a soldier's poncho.
The "round object" appears to be made of lead. The ruler (thanks for including it in the photos) shows it is a bit larger than 1-inch in diameter. So, it is definitely not a bullet. If it came from a civil war battle site, it is a Canister-ammo ball.
Th small-ish iron buckle could be from many pieces of horse equipment, or soldier's equipment. No way to know for sure.
About the brass cartridge-casing:
As Fyrffytr1 said, we need a closeup photo of its base, and precise measurements. Meanwhile... the most common one which is "about" the size of yours is a .52 Spencer Rifle/Carbine bullet's casing.
Friendly advice:
Since it seems you'll be digging a bunch of different civil war bullets in the future, I suggest you spend $12 or so and buy a copy of the "Handbook of Civil War Bullets & Cartridges" by James E. Thomas and Dean S. Thomas. It contains hundreds of closeup photos of various civil war bullets, with their CORRECT identification. (The old obsolete book on civil war bullet IS by McKee-&-Mason has turned out to contain many-many identification errors.)
