The one in between the cups (smaller rectangle) holds my wallet/cell phone perfect, i wear basketball shorts a lot so its more comfortable to put the wallet somewhere. Big one holds my Gatorade since i buy the 32 oz thats fat and short, it wedges in perfectly.
Slots? As in plural? I see one between the cup holders, why do i see several references to multiple rectangles? Are we including the rear section that contains yet another cup holder within as a rectangle?
I always assumed that space was there in case you had a mug with a handle. But rather than make is useful for that single purpose, they cut out a larger rectangle to add to its usefulness.
Mine usually holds my wallet, the phone goes to the left of the steering wheel, the bluetooth goes to the right of the steering wheel.