score:3
To solve your immediate problem, use a cubic volume calculator. Granted, this is not 3D, but it will solve your problem of figuring out whether things will fit or not - as it works in volume, it doesn't matter the orientation.
Commercial shippers use a CBM calculator which works the same way. CBM = Cubic Meter.
You'll have to keep in mind the following restrictions though:
Upvote:1
It's not just about volume, but fitment. While it seems like an easily computerized problem, I am aware of large clothiers that still manually plan their cloth cuts. The software helps the cut planner make the panels fit, but still the human factor is necessary for best efficiency. And they're only working in two dimensions!
So don't expect there to be a program on the app store to help you solve it in 3 dimensions. It's a non-trivial problem.