Before you start packing or even planning, you should be aware of the following.
Vaccinations
Check with the local authority websites what sort of vaccinations you need to have had before travelling to Thailand. The usual vaccinations will have to have been taken 8 weeks before your departure to Thailand. Also, consider the corona virus and taking a test for that before you go.
Travel Insurance
Ensure that you know the specifics of your travel insurance and what it covers before you go. There is a World Nomads Backpacker travel insurance that is described in detail on Lonely Planet that you can consider as an investment.
Flight Details
Make a list of all your flight details so you know when your flight will be and can take your COVID19 tests in time. You can also check the flight availability and bookings. Make sure that your passport, visa and other details are up to date. You can also call ahead to your hotel in Bangkok Sukhumvit and have them arrange pickup at the airport.
Vaping
Something to be aware of, vaping is illegal in Thailand and if you are caught you will be arrested by the Thai police and fined. There is also a 10 years max prison sentence so be careful.