Kay, so I'm an American who checked in to the first leg of their flight earlier today and I just want to let ya'll know that they asked for ALL of my documentation (visa, Thai pass, Covid test, onward travel because it is a one-way, vaccination card - everything!) even though my first leg was a NATIONAL flight operated by a different airline (JetBlue) than the one I'm primarily booked with (Etihad). People have claimed on here that this stuff is only needed for the international portion of your flight but that was definitely not the case for me and I would not have been able to board if I'd ignored my common sense. I was told my docs would be re-checked for the international leg and they were. Both checks asked for my physical vaccination card, so I guess make note of that too.
TLDR : Answer Summary
An American traveler shares their experience of needing extensive travel documentation (including visa, Thai pass, Covid test, onward ticket, and vaccination card) for both national and international legs of their flight to Thailand. Several comments emphasize that it's critical to have all documents ready for each leg of a flight, especially when the airline checks in for both parts or if luggage is checked through to the final destination. The discussion highlights differences in airline practices and the importance of understanding travel documentation requirements for international trips.