Is is your first time abroad? (Thailand)
Dont bring to much clothes because you can get a hold of cheap clothes very easy. The public transport is also incredibly cheap, around 20-50B. I would also recommend to skip the breakfast at the hotell and adventure out in town, a street stal meal can go for just 50-100B. (Highly recommended).
You do not have to worry about dirty clothes, especially when traveling in South East Asia. Wherever you are, you can find a place to wash them. It does not cost much, the price ranges between $ 1-3 for 2 lbs of laundry.
Do not be fooled when you are offered a fixed price by a taxi driver. It is always cheaper to ask about taximeters! Do not be afraid to say no and wait for a new one. There is always a taxi that runs with taximeter.
A bank card with no withdrawal fees within the EU. Good for saving money on the long-run.
Do not make the stupid mistake of not bringing toilet paper. Most toilets do not have it!
Dollar and photo of yourself
Some countries have visa on arrival, in Laos you need to bring a photo of yourself and $30 in cash to recive the visa. It´s allaways good to be prepared!
If you are not the kind of person who likes to bargain for taxi then there are Uber or Grab. They always give a good price. If you think you are being fooled by the local taxi driver, you can always check the Uber price in your app!