It's important to pack the right items for your trek. Don't forget important things, and definitely, don't bring too much as you and/or your porter won't be happy with a load that's too heavy. Here is a list of what you need for a comfortable trekking adventure.

The Essentials

• Shoes - Lightweight hiking boots are great. Make sure they are comfortable and you have worn them in before arriving in Nepal. Trail running shoes will work, too, which are lighter but not ideal if it rains or snow (unless they are made with Goretex)
• Shorts
• Trekking pants
• T-shirts - Lightweight, quick-drying
• Long-sleeved shirt
• Fleece
• Rain jacket  
• Down jacket
• Socks
• Backpack - With a good waist and chest belt; a light one should be enough (e.g. 35 liters capacity)
• Sleeping bag
• Cash - Bring enough rupees to cover your trek. Once you begin trekking, there are no more ATMs (except in Namche)
• Water - 1L bottle should be enough. You can refill or buy new bottles in tea houses along the way
• Sunscreen
• Sunglasses
• Hat

Optional

• Trekking pole(s)
• Small first-aid kit - Band-Aids, Diamox (for altitude sickness), antiseptic cream
• Hand sanitizer
• Toilet Paper - Which you can buy along the way
• Quick-dry towel
• Soap / Shampoo
• Flashlight / Headlight - A headlight is handy at night, especially since electricity comes and goes pretty often
• Dust mask - For dusty sections of the trail
• Camera
• Sleeping bag liner