I have a 2021 C63S cabrio. Last night I picked up a take out order for dinner. I put the two bags on the floor in front of the passenger seat. To make sure the bags didn't tip, I wedged a small box between the door and the bags. While driving I saw this part actually Inside one of the bags containing my dinner. I cannot identify what this plastic/rubber part is.
Can someone identify it?

Those are the pads for your side bins, no?

I am sorry if I was confusing but I believe those are the pads for the centre cup holders at the rear since you have a cabriolet.

As @W205C43PFL said, that looks like the rubber mat that goes inside of your rear cup holders.

Thanks for chiming in as always superswiss! Thanks for confirming for us.

That is it, BUT, how did that part go from the the rear of the car to landing in the bag containing our food on the floor by the front passenger seat? Well superswiss? Lol

Maybe it jumped . Best guess is that it was never actually in there, but lodged somewhere around your passenger seat and it finally got knocked loose.