What are the practical bounds of a minifigure?
Standing

The smallest area you can enclose a standing minifig in is just about 4x4x4 2/3 with the roof on:

  

To reach this limit, you need to use the panels and windows to make room for the arms and more importantly the head, which is larger than a 1x1 brick.

Seated

To enclose a seated minifig in the smallest space, you will need to ensure that you've tilted the body completely forward (i.e. over 90&deg;), and again use panels to enclose the arms to achieve a 4x4x4 box:

  

Note that I've had to use two plates to lift the roof above the stud on the head - you can cheat a bit and lower it one plate if you use a roof with a hole in the correct place - in the photos I'm using a 3x4 tile with 4 studs that comes with the collectable Minifigures, and the head stud fits into one of the cylinders underneath, but the edge of the 2x3 plate won't fit.

Reclined

For a reclined minifig, I used a Slope brick, 33&deg; 3x2 to provide some support, and the smallest space I could fit that into was 4x7x2 1/3, however over the legs it's only 1 1/3 (I don't have all the parts to hand to photo this one I'm afraid, but I have proved the concept with some bricks):



With Accessories

Picking the Wizards Hat and Air Tanks, I was able to enclose the minifig within a 5x4x5 2/3 (one deeper and one one higher than the standing minifig):



Again the minifig is angled to fit in this space so that the rim is horizontal, and once again there's judicious use of panels: 1x2x3, 1x2x1 and 1x1x1 Corners.