I really cannot understand this mindset. What Thailand are you living in? For most people it's a lot better than it used to be, especially retirees. Remember all the harping about 'the good old days'.. well this is extremely similar, without mass tourism, lower prices and also some of the downsides that people forget about, like not having 30 low cost flights every day.
Maybe a (certified) translation of your wife's birth certificate, and marriage certificate. This may be needed for certain things in Western countries.
Although typically a translation can't be too old when using it, so unless you have plans to arrange specific things then it's probably not worth the bother.
Buy at duty free, transfer into Ice Oi Ichi Tea bottle bought from the pharmacy. (Comes with free ice tea).
Tell shop attendant you're only going as far as your first flight because otherwise they're going to spend 20 minutes figuring out if duty free items are allowed to transfer.
* You need a copy of your passport to buy a ticket at the counter. You don't need your actual passport.
* You don't need your passport to board the train.
* Although in Thai law you should always have ID with you. In practice this usually (but not always) means that also a copy is okay, or a Thai driver's license is ok, etc.