The only thing I never have a place for in my Cube are my sunglasses. Luckily with a little bit of tape (& an old visor sunglass clip), I figured out the perfect solution. 

Hey Nissan, can we make this an official accessory? 

File under: shortest post ever.

Just got myself some new license plate holders to replace the gawd awful ones supplied by the dealership.

They are actually chromed metal and cost about $10 a piece.  Nothing too fancy, but they somehow make me feel I've put my stamp on the Cube.  By doing so the Cube feels more mine than before (as ridiculous as that sounds).

I'll upload some pics once my phone is done charging.

Here's a pic.

Since the Cube came already maxed out with alloy wheels, push button ignition, six speakers, and everything, I have been looking for other "accessories" and found Freitag, a Swiss company that makes bags out of used truck tarps, seatbelts, airbags and bicycle tubes. 
http://www.freitag.ch/shop/FREITAG/shop.jsf
I bought a JOE: hi-function midvolume messenger in red and white. It is kind of stinky (truck tarp, you know) but lovable.