Originally Posted by
br2k
I have no checked bags, so that's a non-issue. However, it really sounds like the only way is outside. Not ideal.
You won't be alone. There will be a few hundred other people overnighting landside (there are at least that many air-side overnight on intl-intl connections), along with the usual cast of characters. You could opt for a nearby budget hotel, which would at least afford the opportunity to take a shower, change clothes, maybe grab something to eat, and maybe snooze for an hour or two. There are some eateries within the main passenger terminal building which may be open 7x24, landside on level 3, and a local style prepaid food court down on level 1. The good news is that the domestic flight the next morning is relatively stress-free re: check-in and security. No dealing with immigration, obviously, so assuming OLCI/kiosk and no checked bags, you could leave for the airport at 07:00 ~ 07:30, assuming you're staying in nearby Lat Krabang.