I'm going to provide a listing here of some recommended apps to pick up before you arrive in Thailand. These can be useful in a variety of situations for various platforms. This is not a complete list and their availability on your device is subjective.
There are a variety of ride hailing apps available in Thailand. They all comes with their pros and cons to them. Download a few and see which ones you feel more comfortable with.
TukTuk travel app - This app will help you to hail a tuktuk at a pickup locations similar to other ride-hailing programs.
All Thai Taxi - This app will help you to hail a taxi for your trip.
Grab Taxi - This is another taxi hailing app which is used in the country.
Google maps - This map app also shows the major tourist destinations and routes to get between them from various transportation. Bringing the app into street view helps to see the surrounding area.
DLT Check In - This app is for those unfortunate times where you may have had a taxi encounter go bad. This app is a way to report the taxi drivers.
XE - This app helps you in finding the common exchange rates with Thai baht and your local currency in the country. Some transaction locations may provide higher or lower rates than what is provided by the app. Those specific bank apps should be used in those situations.
Super Rich - This is a banking app for one of the best exchange banks around.
Check my Trip - This app will help you to keep track of your flights and schedules.
Google Translate - Translate Thai to your language and back. This also has a camera feature to allow you to translate signs.
Line - This is a popular communication app in Thailand and it's free to use.
The Bangkok Post - Highly recommended for keeping up with local events which may impact your vacation.