Here are 5 'keychain objects'. Each one is on a beaded chain so you could add it to your key ring. The rounded teardrop shaped ones are shoe horns to help you into your shoe. The triangle/pointy ones are likely to be book marks, as the little point goes behind a page & the long area goes on the other side kind of like a paper clip. The rectangle is just a key-tag shaped Amy Rose keychain. They're all made with 'aged metal' which is kind of textured & has black patina over it. It's also notoriously hard to photograph. You can hardly tell which character is in the disk at the top of each item. These are early classic items. 

In the gallary there are more metal keychains! 
With a modern one sneaking in there to the side. You can see a Tails clip with 'looking out' Tails & his name. Knuckles is on a 'flat card' style multi tool. The marks on the edge are a ruler, the square hole likely picks the lids off bottles...but what does the slot & the other jagged hole do?
The modern keychain is thick metal with a stamped out & texture detailed modern Sonic. It has the "Welcome to the next level" slogan at the bottom & a sturdy rotating clip. All the 'aged metal look' ones here are likely a set of some kind, all released at once.

There is also a better look at the Tails Rotating Keychain. There were 3, you can see the others here on other pages of Keychains. (Sonic & Eggman) This cool shot though, clearly shows the slogan "I Like Your Style", the Segasonic logo & that the character is shown as a raised design both front AND back, which is pretty unusual because stock arts don't tend to also have a 'back view'. However, this nice detail makes the spinning around gimmick even better for these keychains. (Sort of too bad it uses the odd 'big nose Tails' art, though)