Clothing/Shoes/Weather Gear: Sweaters! Lots of them. I brought 2 sweatshirts and lots of longsleeved shirts- I was in a constant state of being frozen. I recommend several sweatshirts and lots of fleece, a good hat, scarves, etc. for nighttime. During the day its usually nice but at night I was cold.
You will want to go to the more remote places. Make sure to bring good gore tex rain gear, excellent hiking shoes. Remember that you are at altitude. The moment the sun goes down it is very cold. Do not spoil your trip. Be prepared and enjoy.
Toiletries and Medical Supplies: Bring everything that you think you might need. Spend your time enjoying this unique space instead of hunting for medicine.
Miscellaneous: Remember that you are at high altitude. Make sure that you acclimitize before heading off to even higher altitudes.