Sukhumvit to Suvarnabhumi Airport by BTS and Airport Rail Link
Bangkok road traffic is heavy throughout the day, risky in the commuters rush in the morning. The wait for Grab cars and Grab bikes are typically 20-30 minutes at all hours, then stuck in traffic for another hour for 5 to 7-mile rides. Road option is time consuming and unreliable to go from Sukhumvit to the airport.
For early morning flight I would walk from hotel Maison to Ploenchit BTS station, take a ride to Phaya Thai station, only 9 minutes. Switch to ARL, only 25 minutes to the airport with no chance of traffic jams on roads. Add 10 minutes walking, buying tickets and waiting at each station, I got to the airport in 55 minutes along with the morning commuter crowd.
After so many long waits for Grab cars and traffic jams, I would take the BTS to FIWFANS girls in Ratchada and Huay Khwang. From the nearest stations instead of walking, I would book Grab bikes to their hotels. It's the quickest and cheapest means to go places in Bangkok.
Good tip to have small bills in hand for BTS
Or buy food / drinks at the stores for change. You can also buy tickets from the machines.
I am not aware you can board Airport Rail by tapping credit card like Singapore's Metro. Ticket counter gives you a paper ticket like a business card which you insert into the gate.
I don't want to pull out credit cards and use them in too many places on the road. They can be easily lost or cloned.