It's not a long ride to Pattaya why not just hunt up "authentic Thai food" after you check into your hotel room?
You are not driving yourself from Don Muang are you? If you have a driver he or she may have a suggestion but if you are asking him out of the blue he may prefer to just bring you directly to your hotel.
Are you trying to kill some time until check in at your hotel? If you arrive early at your hotel most hotels will store bags for you until the rooms are available. Then you can check out food places in Pattaya area.
In over 20 years the only stops I have been on between Bangkok and Pattaya have been gas stations for toilet breaks.
Maybe someone will come up with a suggestion.
(My opinion.) If you are using a "random" driver to bring you to the hotel in Pattaya - do not leave passport, money or expensive electronics in the van when you go to eat! Always keep passport and money with you unless locked in a safe.
Its only three hours at most from the airport to Pattaya depending on the traffic and your chosen method of transport, once you are out of Bangkok there are plenty of options along the route including most of the usual fast food options, lots of places serving Thai food but none that off hand I could thing of recommending, You could always ask the driver but if he has another booking after dropping you off he may not be able to stop. What until you get to Pattaya.
If you're desperate to try Thai food on the journey back to Pattaya, just ask the driver to stop at the motorway service. Lots of Thai cafes there, and if that don't take your fancy there's McDonald's and KFC.
DM to Pattaya is 2 hours at most by car/taxi.
I think a lot depends on how you are travelling....if self drive there are hundreds of options.
If you have a taxi or driver then you are down to paying for the extra time.
On a straight trip, you are most likely to go on route 7.
Your choices on that are the PTT gas stations which have a plethora of junk food and maybe a basic food court with noodles and something on rice. They are usually accused via the frontage road, the turn-offs onto the access road have been greatly reduced near to Pattaya with the opening of the new tollbooths.
Just around the Chachoengsao junction there is a large service area.Apart from the fast food outlets there are various eateries offering basic Thai dishes..... some surprisingly quite good....a lot is served buffet-style so you can see what you are ordering.
HOWEVER......If you want to check out the coast, take the new Bang Saen junction off motorway 7 which heads directly down the Bang Saen beach....about 10 to 15 minutes ... There you will find more seafood restaurants than you can shake a stick at. Sitting on the deckchairs on the beach is not recommended as it is way too expensive for the food you get. There are loads of eateries of all types and price ranges. Weekends the traffic gets very heavy.
You could try a restaurant at Ang Sila.
After Bang Saen you can continue on to Pattaya along Sukhumvit highway, about 45 minutes.Edited: 15 March 2018, 00:36
PS - If you don't take the motorway, you can take route 34 expressway from Bkk; the Bang Na -Trat highway. On this route, you could come off the elevated expressway at some point and travel at ground level or follow the expressway to where it ends ends at Chonburi, from there you follow Sukhumvit to Pattaya (past Bang Saen, Bang Phra through Sri Racha Laem Chabang etc. You will see eateries either by the road any of the turnoffs to towns along the coast all of which will have eateries.
This route is a large highway but the traffic will ensure that from Chonburi on, it is slower than the motorway.
(BTW the key to a good roadside eatery is plastic chairs and stainless steel tables)