I have AIS prepaid unlimited data (฿1200/year) on my old phone Speedtest 10 down/20 up (not sure if throttled because I’m a dirty Farang but only 1 bar reception), 60 down, 6 up on True 5g postpaid. Also 1 bar reception
they changed that in 2019, that you don’t if you’re returning to the same home, however, some immigration offices, including Bangkok, are enforcing again that you need to keep doing your TM 30s.
Most of the Thai individual health insurance you get is going to be useless. Besides excluding pre-existing conditions, look at the amount it pays for hospitalization per day. Usually to collect the full amount whether it’s 500,000 or 3 million baht maximum per year, you would have to be in the hospital for 365 days. Often what you were going to collect for major illness, is a little more than the premium you pay in a year, unfortunately, you may as well self – insure.
Try your thai sim; sms may work. If not try the app and text them to ask for international service. If yiu need to top it up you can use mobiletopup.com
they used to be the most farang friendly, but that depends on the branch. Beware the 50K฿ transfer limit though. I still bank there, they are hounding me to come get my pictures taken, not sure if that will unlock the deposit limit. It was imposed because most banks didn’t meet some new KYC requirements. Most all thai banks don’t want to open farangs’ accounts without work permits. Other issue is they want residency certificate, need TM30 and have done a 90-day report (Bangkok immigration), and a workaround, getting certificates from US embassy (if you’re American) just became unavailable.
 Leaving Bangkok? Why would they care? Are they going to make you stay? And I wouldn’t think the staff or you go through security or connected with customs or immigration,
Being more concerned about you having something dangerous. I’ve never had a problem in Thailand, but at the new, awful Berlin airport last year, I had a lot of tech stuff, they were fine with that, but I had a plastic bag with two power banks, and a watch. They stopped the line, sent the other people to another Q, and called the police on me. They asked me what I was doing with a watch and a power bank. I almost missed the flight, and I will never fly through that airport again.