5 sets with 3 key-holders on each. These are the type where you clip the key or another ring to the bottom, rather then on a ring. Here you can see each of the characters that appeared, as this is a Sega booklet photo. These were likely to have been released right after Sonic 3 came out in Japan.

These are old-style Amy Rose key holders.
Similar to a key-chain, but not quite. First, they're all the same Amy head, just with different colored backgrounds. Each plastic piece is attached to the central ring, and has a loop at the bottom. You can attach keys or charms to this little loop.

Photo by Nick M

Here's another good close up so that you can get a better look at the Sonic & Eggman key tag sets. All of these work exactly the same and came with a red, green or yellow background, all with the same face on the front. Sonic looks quite decent here, and Eggman looks mad. Photo by Nick M.

Photo by Rhia

Discovered by MrCalistine

You've seen these before in a group shot, but here's a better look. They're really 'plastic' looking Knuckles faces, in red, green & yellow w/raised details. They're more of a key organizer than a regular keyring. Using 1 head for each different item, you can identify it quickly. You'll find these with Sonic, Tails, & Amy heads as well.