A fleece jacket, down jacket and thermal underwear are a must, as the Himalaya gets cold above 3000m any time of the year. Also take two pairs of long pants, two or three T-shirts (synthetic fabrics – not cotton – that wick away sweat), and another warm jumper or light fleece.
Footwear requires lightly broken-in boots, trekking socks, and sneakers or sandals for evenings. You will also need a raincoat, gloves, woolen hat, sunhat and polarized sunglasses. A good sleeping bag (rated to -20°C/0°F) is essential; if it’s winter, a thermal liner makes it extra toasty.