Depending on the services that you are being provided with on the mountain they may well be suitable for the entire trip (but this does depend on your ability to pack things efficiently)
[ ] 45-55 Litre rucksack will suffice for the trek in. The Fast Alpine by Montane and the AMG 55L by Mountain Hardwear are examples of classic ‘no unnecessary frills and extra straps’ sacks that are perfect for the trek. Depending on the services that you are being provided with on the mountain they may well be suitable for the entire trip (but this does depend on your ability to pack things efficiently)