A screw in the boot
 

Why, you filthy minded so and so! No, I found these in my boot this morning and can't figure out where they came from. Any ideas?

In your shift boot? Please elaborate.

I'm thinking he's using the word "boot" for the trunk.

These little gizmos hold in your carpet, keep things in place and are used all over your car. Look under the front bumper and in your wheel wells and you'll see more of them. Look around and you'll see where it came from inside your trunk (or boot, as you call it).

Yes, the trunk.

..........

The one on the right is used to hold the side covers on the trunk. That particular one looks like the one that screws down the cover over the tail light access.

The one on the left looks like one of the push locks for the side covers. If it is, you should have a larger plug that has a hole in it. That pin goes in the hole to make the plug hold tight from behind.