Sometimes you need to pack a suitcase.
One way of doing it would be to have a list of how many socks, shirts etc. can the suitcase hold, then prepare these items and pack them into the suitcase. This should work, I think, but there are a few problems. First, you need to have this list ready for each suitcase. Second, well, it would be difficult to prepare such a list due to the unstable nature of clothes: wrinkling, moving, and in general the tendency of not having a steady shape.
However, the main problem with this method is that it takes a lot of time. You need to constantly check the number of items against the list, write down how many you have etc.
Another method would be to just place a big pile of clothes on the sofa and then pack them into the suitcase. This sounds a bit unnerving, I am aware of it. The sheer simplicity of it makes it sound like a joke. But let me assure you it works!
The real beauty of the second method is that if the pile of clothes does not pack into the suitcase you make very fast decisions as to what stays out – I am telling you this from experience. Of course, it wouldn’t work if you let someone else pack it for you. Then you’d probably stick with the first method.
The question is: do you trust your ability to execute and make real time decisions? If so, you could save yourself a lot of precious time spent on planning.