Cloths to bring in Thailand
You don''t have to bring jumpers or jackets, they are useless in Thailand as it is always warm. Only if you are visiting the North of Thailand during the winter season, a jacket can be usefull in the mountains.
For the rest of the seasons bring light cotton cloths. Jeans are not very comfortable as they are heavy and warm, and take long time to dry.
Sunglasses you better bring from home, as the quality will be much better than in Thailand. All other usefull things like toothpaste, shampoo, sunblock etc. is widely available.
If you are planning to stay in low budget ho(s)tels, than it may be wise to bring a musquito net and repellent.
Bring sandals as footwear, unless you will be tracking of course, than you should also bring boots or trainers.