What have you stuffed into....

LOTS!

Including a 3x5 office desk, with legs attached, plus 2 smaller desks and a LOT of boxes. Then drove it 3.5 hours.
I moved much of a 10-person office in it from Jan to March (ended weekend of Sanitarium, unloading the last load an hour before I showed at World Toyota on Friday.
The cargo deck and handtrucks in my box that weekend were NOT for show, but function.

5' tall chest of drawers
several boxes of stuff
Tall lamp

Could still see out the back window.

I like what someone called the xB2 . . .
A TARDIS!
http://en.wikipedia.org/wiki/TARDIS

In your xB-2's cargo hold . . .

If you want more space for a flat load:
Have the rear seat up.
Pull the front passenger seat all the way forward.
Remove headrest, then lay the seatback all the way back.
Now, lower the rear seat forward and you'll see that it sits flat higher than the seat. So, you can have that space for flat storage too.