What do I need to carry while climbing Kilimanjaro?

Because you have the help of your porter crew to carry your things between the camps, you carry only a day pack (small backpack) on the trail. This pack should have everything you need while hiking to the next campsite. Normally, you would include the following things in your day pack:

Be sure your day pack has a waist strap and good back and shoulder support.

To pack your day pack efficiently, you should use plastic bags to separate items based on categories.  For example, small bottles such as prescriptions, sunscreen, lip balm and hand sanitizer should be secured in a zip-lock type bag.  Extra layers of clothing should also be put into larger bags.  Paperwork, such as your passport and insurance documents into another bag. 

Heavier items like water and electronics should be placed close to the midpoint of your back to keep your center of gravity in-line with your spine.  Placing heavy items near the top, bottom, left, right or rear of your day pack will cause you to lean forward, back, or to the side.  

If your day pack has compression straps, tighten them so that your items do not move around as you walk.  Lastly, be consistent as to where you store your items (main compartment, side pockets, pant pockets, etc.), so that you do not fumble for your items when needed.  A medium sized backpack, with the capacity of about 1,800 cubic inches (30 liters), is appropriate.

Everything else is put into a large duffel bag. You will not see your duffel bag from the moment you hand it to the porter in the morning to at least lunchtime, and maybe not until the end of the day.