Can any bro n sis here give latest inf about the situation there. Many of our guys are over there. Any guys from Thailand here can give inf as in how the tourist there can travel out of Thailand?
A lot of tourists will try to go Phuket or Chiang Mai to take flights out. In my opinion, if its me trapped in Bangkok right now, I wouldn't go these places to take flight out. Because too many people will think the same as you and these places are tourists spots. The tourists there will add on to the traffic of tourists which came from bangkok.
There are a few alternative avenues, providing you can get an air ticket back from these origin locations
Chiang Rai(Northern side)
Ranong (Southern side)
Nakhon Si Thammarat (Southern side)
Ubon Ratchathani (North East)
Ubon Thani (North East)
Going to Krabi is already quite near to Hatyai
Narathiwat and Surat Thani i would tend to avoid as during these time of confusion, its better to avoid such place due to their past militant bombings happenings. (You never knew what those militants would take advantage of at this point of time)
Taking the bus would be jammed packed with many people. Could try hiring a private car with chauffeur to drive to these locations and the price could be easily 3000-7000baht depending on location and timing.
However I don't think many people would be using the above locations to travel out of Thailand as majority of tourists mostly knew about BKK, Phuket, Chiang Mai. Only those who go thailand often will know that the above places has avenues to get out of the country.
This is the 1st contingency plans I have if I am in Bangkok and the airports are closed.
The last contingency and the longest time taken will be to travel via connecting buses to Hatyai and then to Malaysia to take a next flight back singapore or even take bus via customs to Singapore.