Wow so sorry about the challenges for your son getting gluten and dairy free options. I understand it can be so difficult to find safe foods for kids with allergies. Luckily my son loves sushi and lots of rice dishes (born on Oahu so raised on rice lol).
When I traveled with him as a young boy, I often packed half a suitcase with safe foods like rice mix, safe cereal, etc. Years ago, Target in Kapolei didn’t carry Earth Balance (dairy free butter type spread) but I found it at Down to Earth (for of course a couple dollars more than what I pay here). Also, I’d have safe snacks in my carry on, since it takes a whole day for us to get to Oahu from the east coast. Once in first class, the two meal choices were both unsafe (a pasta dish with cheese or a chicken dish with dairy), but the super flight attendants said coach had chicken teriyaki with rice. Happy kid got a meal.
I’d definitely pack some safe things.
Last trip I took just my kids and my niece, and we did Door Dash a bit. We got sushi party platters from Genki Sushi delivered, Sushi Bay delivered, and Pearl’s in Kapolei (Korean BBQ place). I’m pretty sure Pearl’s has many gluten free options (if soy sauce is safe though?). They loved the chicken and kalbi. Grilling meat and having a side of rice is often what we do too.