Thailand packing list
What you need to bring with you depends on the time of year you're going and what parts of the country you're visiting. I went during the winter and spent the majority of my time in the south at the beaches.
There aren't many places in Thailand where you need to "dress up". You can get away with pretty casual attire in most places. However, if you are planning on visiting any temples you will need to bring either pants or a long skirt and a top that covers your shoulders and chest. They are very strict about this and will not let you into the temple if you are wearing improper attire. Some are stricter than others so I would suggest that your clothes also be loose fitting. One of the temples we went to considered leggings or workout pants as too "sexy".
This is what I brought for 2 weeks:
5 pairs of denim shorts
5-10 tops (tank tops or short sleeved)
1 pair of jeans
2 pairs of what I like to call "MC Hammer pants",but they're basically lightweight joggers
1 maxi skirt
1 maxi dress--I like these because they're versatile but also don't take up too much room
1 light weight jacket or sweatshirt
1 rain jacket
3 bathing suits
3 pairs of sandals https://www.whitemountainshoes.com/ I like White Mountain's sandals. They're super comfy, but cheaper than Birkenstocks.
1 pair of slip-ons/comfy walking shoes
Daypack/backpack: https://beistravel.com/products/beis-backpack-black I like this backpack because it's really easy to get to your stuff and keep it organized and has big water bottle pockets
1 small purse/bag https://bit.ly/2t1VHcl I like this bag by PacSafe because it's small, but still holds everything you need and is very secure.
Camera and accessories
1 quick dry towel
Some type of hat for the sun