@Suntan12- I have to say that I always try to pack about a week in advance.I will usually pack from a list that I put together and this helps me to avoid forgetting certain things.
It also keeps me from packing too much. The same way that you should use a list when you go to a grocery store, I think you should also create a list when you are going on a trip and if you give yourself a week in advance you will be well prepared for your trip and will not stuff your suitcase at the last minute.
I hate that frantic feeling of packing at the last minute and often pack more than I need because I did not plan properly when I do that. I think that planning ahead is the key.