All the parts in the kit should be installed.
they are to prevent squeals while braking.
Maybe the last time the brakes were replaced, someone forgot to move the
parts over to the new pads.
Some after market pads do not come with the shims/clips, so you need to
transfer them over.
But the honda pads come with all the parts, so you can discard the old
parts.
Get a hold of a factory service manual for details on the brake pads
installation.