I pack in stages.
about 60 days out I pack our toiletry bag. I buy all new stuff. (We never worry about running out of something.) Then when we get home all these go on the shelf for our extras. It also helps to spread out the expense a ways before the trip. I keep a sheet in the bath that has the things highlighted that I need to add at the last minute.
About 2 weeks out, I pack our back pack and our re-usable souvineers. Double check plenty of film and extra camera batteries, etc.
About a week out, pull out all clothes we plan to pack. Pack what I can, set out traveling clothes. then actually finish packing the afternoon before the trip. Pack van the night before trip.
But do what is best for you and your schedule!!
~~Beth