Side sill plugs
 

I was poking about in the trunk today after taking the plastic of of the cargo tray that the dealer didn't do, and I noticed a little bag under the tray. The bag had side sill plugs in it that the dealer didn't see it put on. So I put them in.

Sorry, I am not following you. What are cargo tray side still plugs? Do they keep the cargo tray from moving around in the trunk?

I suppose I wasn't detailed enough. I took out the cargo tray, then the trunk tray and the baggie was in the tire well foam.

The covers to under the car near the rear in the side sills.

still not following.

maybe a picture?

This is all I got for now.

Rocker panel drain plugs?

The bag says

I guess you could call them rocker panel drain plugs to. I just used the words from the bag they were in.

Those are plugs for the holes used to chain down the cars during transport on the boat.
They were neglected by some dealers when the first models were sold too.
May be able to find the posts from early on.

A lot of dealers in the "New World" don't have a lot of experience anymore with cars manufactured in Japan.
They get most of their imports from plants in Ohio and Alabama.

I had the same plugs in the trunk of my 2018 BRZ. I guess both the PDI and the previous owner didn't care enough to notice. I've put them into their holes.

If you're tracking the car and towing it, those are convenient holes for T/J-hooks ;)