Machine Monkey I hope you're reading, this would be a perfect place to fit a twin cup/bottle holder. The base of the actual holder could fit in this slot to secure it, along with the base that goes over the armrest for extra support.
It would be easy to lift out to gain access to the cubby hole behind it?
I used to keep my phone in it until I kept leaving it in the car and it was on show to any and all. Also I found it was a little too far back to be useful for quick reference.