The kit you use for a two week trip like the TGO Challenge must be well tried before you go, half way across Scotland is not the time to find out that something is no good! Take equipment that you are used to, remember that lightweight is good but comfort is better, you will be warm enough when walking as long as you stay dry (beware of high passes and tops) but camps can be cold, be sure your sleeping bag will keep you warm. Food is heavy; plenty of shops or food parcels on route will help here, you do not need to carry much water, there are many small burns that will supply good water if you are careful.
Here is a full list of the kit I used for the last three years, the total weight in 2007 was approx 13Kg (Pack weight 10Kg Clothes, boots etc 3Kg) plus food.