I will assume that davidgrahammd is talking about Narita Airport station, since Narita Express does not stop at Narita (city station) except for early three trains, N’Ex no. 2, no. 4, and no. 6 departing before 9 a.m.

At Narita Airport station there is only small shop selling drinks, sweets, snacks, etc. The shop at Narita Airport station (Kiosk) may sell sandwich or other pre-packaged bakery goods, but I think that will be it. I really do not think the shop at the airport station sells bento.

At the arrival floor of NRT, before heading to the airport station, there are shops selling drinks and snacks. I never really looked carefully so do not know for sure, but some say it sells bento, I have no idea about selections and amount they stock.

I know if you go up to the departure level, then many restaurants and shops do sell take out bento type. Some has sign indicating can take it through the security and onboard the flight.

My guess is that selections at the arrival level shops are limited. Have to go up to the departure level of the terminal for more variety in selection.

P.S.
Bento sold at train stations is called Ekiben (駅弁) and bento sold at airports is called Soraben (空弁). Ekiben is well established term which has been around for long time, but Soraben is relatively new term, maybe Soraben started to appear 10 – 15 years ago.

However, on 1988 the company which had exclusive right to operate shops at JR stations back when JR was government entity obtained registered trademark on term “Ekiben” and now only this company can sell bento at train stations under “Ekiben” and other companies at train stations have to use term “Bento.”

Japan National Railway become private entity JR on 1987 and this company lost exclusive right to operate shops at JR stations, and obtained the registered trademark on “Ekiben” so that nobody else can use the term “Ekiben.”

“Ekiben” was already commonly used term and many thought registered trademark should have not granted.