How I used to pack:
A list, three days of thinking about what else not to forget, packing your bag a day in advance, putting in the right amount of clothes.
How I pack now: an hour before leaving I toss in whatever clean underwear, t-shirts, and socks I have, check that my documents, money, and meds are all there, and order a taxi 15 minutes before the train.
The main thing is not to forget the tea.