Here’s my packing list for the Annapurna Base Camp trek. If you do forget to bring anything you can pick up most essentials at shops in Ghorepani or Chomrong. There are plenty of shops selling trekking gear in Kathmandu and Pokhara.

Clothing

Long trekking trousers/leggings
Trekking shorts/skirt
Thermal base layers (top and bottom)
Cool trekking socks (ideally at least two pairs)
Technical tops (at least three)
Underwear (at least three sets)
Warm trekking socks (ideally at least two pairs)
Warm jacket (fleece or similar mid layer)
Waterproof jacket
Waterproof bottoms
Warm hat
Sun hat
Warm gloves
Trekking boots – make sure these are broken in before you travel.
Spare laces
Flip flops or other lightweight footwear

Equipment

Backpack with cover
Sleeping bag – suitable down to freezing
Sleeping bag liner – for warmer nights lower down and extra warmth higher up.
Map – you can easily find maps in Kathmandu or Pokhara.
Compass
Water bottle or bladder
Water purification – steripen or tablets. Or you can buy water at lodges, but this will cost at least $2 per day.
Torch/head torch and spare batteries – For trekking before dawn.
Trekking poles
Sunglasses
First aid kit
Blister kit
Duct tape
Smart phone
Kindle/books
Chargers and travel adapter
Penknife

Other

Whatever toiletries you need
Travel towel
Washing powder
Toilet paper
Antibacterial gel
Insect repellent
Snacks – being British I took Kendal mint cake.
Sunscreen and chapstick.