How to calculate best position/rotation of small objects in order to stay within the bounds of a large box?

Hey,

I'm playing around with an idea where I have a number of small objects placed onto a tray (lets say a flattened cube). I would like to find a way to lay the objects out on the tray with equal spacing between their bounds and also stay within the tray's bounds. I'm only concerned with the X and Z axes here so you can imagine that I'm looking at this scenario from the top-down view, and so the objects can only be rotated along their Y-axis. I would like the objects to have rotations at 90 degree intervals (ie. angle % 90 = 0). I am trying to create a script where I can, for example, press a button which re-arranges the objects on the tray in different, random configurations each time.

Any help with this would be great. Thanks