For summer months – cotton clothing and light woolen clothes for evenings and mornings. You may also need a raincoat & a small foldable umbrella.
For winter months – Heavy woolens, fleece jacket, Rain & wind jacket. You may also need warm hand gloves and earmuffs depending on the places you will visit.
Shorts are fine for hiking and walking around town. You may not wear shorts and skirts in government offices, Dzongs, Museums, national monuments and other public buildings. You must wear appropriate clothing that covers your knees and shoulders when you visit those places.
Sunglasses
Hat/cap for sunny days
Insect repellent
Sunscreen
Reusable water bottle
First aid kit containing lip balm, antibacterial/hand sanitizer gel or wipes, antiseptic cream, etc.
For Trekkings
Sleeping bag all season and pillow (It can be hired locally)
A comfortable medium-sized backpack/daypack to carry things you will need during the day
Sturdy Hiking/trekking shoes (well broken-in as new ones will be uncomfortable and often cause blisters)
Lightweight trekking pants
Trekking shorts
Underwear
Windproof rain jacket/raincoat
Rain pants
Fleece top/sweater
Sandals/flip-flops (camp shoes to relax your feet after a long hike)
Wool socks
Small travel towel
Hiking poles (recommended)
Reusable water bottle
Gators
Sunglasses
Headgear for sunny days
Flashlight / torch / headlamp
Small foldable umbrella
Camera with extra memory cards and batteries
Powerpack to charge phone and camera battery
First aid kit containing lip balm, sunscreen, Insect repellent, Aspirin, Ibuprofen, Throat Lozenges, bandaids, plasters, blister patches/moleskins, tape, antibacterial/hand sanitizer gel or wipes, antiseptic cream, rehydration powder, rehydration powder, water purification tablets, etc.
Emergency whistle (some backpacks come with whistle)