You don't need a fancy pack

Kilimanjaro porters on Barranco wall
If you're using porters to carry your gear on Kilimanjaro (which is the standard practice), you don't need to pack your stuff in a hiking pack with a fancy suspension system... Your porter will more than likely put your pack full of gear inside another larger pack or basket, along with a little of his own stuff and some more group gear. Often he will choose to carry this enormous load on his head rather than his back. We've seen porters walking by with a client's expensive hiking pack balanced on their head, hip belts and shoulder straps dangling down unused.

Many companies recommend packing your gear in a lightweight duffel bag. This kind of bag is more convenient for air travel too, as it doesn't have as many dangling straps to get caught in a luggage conveyor.

You should bring along a comfortable day pack that you will use to carry water, rain clothes, camera, etc. during the day.