Do I need a heavy coat?

No. Even in the north of Thailand during winter, a light fleece is enough. Leave the puffer jacket at home.

Will my laptop fit in a 40L bag?

Yes, if you choose a bag with a dedicated tech compartment. Just ensure it is under 15 inches to keep the bag profile slim.

How to Pack for a Month in Southeast Asia with Only a Carry-On

Limit your luggage to a 30-40 liter backpack to avoid checked baggage fees and move quickly through crowded transit hubs. Pack only 7 days worth of clothing and plan to wash your items locally for about $1-2 per kilogram.

Select the right bag. Use a 30-40 liter backpack that opens like a suitcase (clamshell style). This eliminates the need to dig through your entire bag to find one pair of socks.
Adopt the 7-day rule. Pack exactly 7 days of underwear and socks, and 5-6 lightweight shirts. You will be able to find a laundry service on almost every street corner in Southeast Asia that offers next-day service.
Prioritize quick-dry materials. Avoid heavy cotton or denim. Bring moisture-wicking synthetic or merino wool shirts and shorts that dry overnight after a hand-wash in a hostel sink.
Minimize toiletries. Only pack 100ml containers of essentials. You can buy shampoo, soap, and sunscreen at any 7-Eleven in Thailand, Vietnam, or Cambodia for a fraction of the cost you'd pay at home.

Do I need a heavy coat?: No. Even in the north of Thailand during winter, a light fleece is enough. Leave the puffer jacket at home.
Will my laptop fit in a 40L bag?: Yes, if you choose a bag with a dedicated tech compartment. Just ensure it is under 15 inches to keep the bag profile slim.