The basic idea of your kit is to keep you warm, dry, protected and comfortable from the sun and rain. The main principles are:-
A duffle type bag for general use and leaving gear in Nanyuki, A Rucksack for a porter to carry your kit on the mountain and a small pack for carrying items with you during the day.
Clothing and footwear for travel to Kenya and prior to/after the climb
Waterproof layer to keep off wind/rain. An umbrella can be very useful.
Layered system to keep you warm on the mountain- body hands & Head
Sturdy trekking boots, Flip flops/sandals
Warm sleeping bag and camping mat to get a good nights sleep
Water bottles and favorite high-energy snacks
Suncream, anti-malarials and a small 1st aid kit to allow you to wash and maybe stave off a headache or blister (leaders will have a larger group one)