After a bunch of Belgian students got thrown off a RyanAir flight because one of them had oversize/overweight luggage, it seems RyanAir produced this little video (I can't vouch for the authenticity, found it on a Dutch news site).
YouTube - master-packer
Nice one, actually. Worth watching....
And yes, I always stuff socks into shoes (if I need to carry a second pair).
Otherwise, they're always useful to 'buffer' fragile or odd-shaped items.
But I did like the idea of leaving half of shirts, T-shirts, trousers, etc. outside the suitcase until the last moment, then folding them in. Nice idea for avoiding sharp "luggage" folds.
CJ