Luggage
Sturdy and a waterproof bag
Day pack (a 30 litre bag is the ideal size to use as a day bag, as this will fit your camera, a sweatshirt, a waterproof jacket, a bottle of water and any other miscellaneous items that you need to take with you in the day)
Clothes
Hiking boots, cargo trousers (trousers made from a quick-dry material and with lots of pockets are best for trekking), lightweight down jacket, quick-dry shirts, waterproof jacket, merino base layer, thick socks, comfortable hut clothes, trekking pole (using one or two poles can minimize strain on the knees, and help with balance too), cap/sunhat, woollen hat, gloves and scarf, bandana or light cotton scarf
Other
Sunscreen, wet wipes, tissues/toilet paper, water purifier (having a high-tech steri-pen or even just simple, cheap chlorine or iodine drops will make practically any water safe to drink), head torch (for reading in the evenings, midnight trips to the bathroom, or pre-dawn treks to catch the sunrise), quick-dry towel and sample-size toiletries