Just came back from a Bangkok to Lao visa run. Flew AirAsia to Vientiane. Got ticket (actually itinerary PDF) and boarding pass through their website.
200 baht metered taxi from lower Sukhumvit to Don Mueang Airport.
At Vientiane, handed in pre-filled-in visa on arrival form and 35USD only to see that the visa fee was now 40USD for everyone except Chinese who I think only pay 10. So gave an additional 200 baht to cover the difference as I had no more US currency. Still cheaper than the eVisa which is about 51USD, and line still moved fast enough.
Walked out front of airport and turned right seeing shaded seats in a pickup area. A sign said there was a bus stop some meters ahead, which there was along with a waiting small bus. Paid 70 baht for a ride into town, telling the conductress my hotel. The bus stopped at a bus stop just a short walk from it.
I hadn't booked a room ahead of time and it, a backpacker class hostel, had no vacancies. So walked a few blocks and finally checked-in at an alternate after hitting a couple more fully booked ones.
After check-in, walked to a nearby big yellow TPlus office and bought a 7 day 11 gig SIM card for about 200 baht. Paid with a 1000 baht note and got a big wad of Lao kip in change. This actually came in handy for later small purchases. In general, every time I made a baht purchase and got Lao kip in change, I always underpaid by a small amount according to the current exchange rate.
Not being sure how to get around town, my hotel suggested I download an app called inDrive, which works very similarly to Grab. It made consulate and airport trips pretty much hassle free.
Before my trip, I had made a morning appointment at the Thai Consulate, as now required for visa applications, and brought a downloaded and filled-in application and photos when I went there. This was also not too crowded and the line moved fast.
Passport pickup was two days later beginning at 1:30pm. I wasn't in a hurry so didn't get there until 2:30. I was literally the only one for pickup as one of the staff said the crowd had come an hour before.
My next day early morning flight was also pretty smooth, though I checked out later than I wanted because no one was at the front desk at first, and my driver took a few minutes longer to arrive than the inDrive app said. I ended up getting to Vientiane airport after check-in for my flight had closed, but after a bit of pleading still got my boarding pass. And at the gate there was still a line of people boarding, so all was fine.
When I got back to Bangkok, since I had the time, I thought I'd try taking a train in rather than a taxi. It was quite a long airport walk, though, from the terminal to the SRT station, but plenty of signs pointing the way. Basically this was taking the SRT Red Line from the airport and going two stations to Laksi, then transferring to the MRT Pink Line for a couple of stations, and from there transferring once more to the BTS Green Line. The SRT uses those small wooden MRT style ticket tokens, but the Pink Line accepts a Rabbit Card, so I was able to pay just one time for Pink and Green.