Hi Abby,
Yup, I'm obsessive too. I start packing usually a week before we leave. I am an amputee and find that if I leave everything until the last minute the strain of being on my feet all day doing the last minute packing combined with trying to hoof it through the airports makes me so sore I can't walk for the first couple of days of my vacation and this would apply not only to amputees but anyone who has arthritus or a history of sore backs or knees.
Even if you don't have medical issues to worry about it is just so nice to spend the day or so before you leave, up-beat and full of excitement for the holiday rather than in a frenzy of last minute shopping, laundry, ironing etc.
My biggest problem with packing early is trying to get my daughter to stay away from the suitcase once it is packed, she has a habit of stealing her favorite stuff which has been packed for holidays back out of the suitcase to wear to school LOL