My one son is super picky, I have booked several ADR, and some of the menus have very limited kids options.......do they all have ppj even if its not on the menu? Hes pretty well a nugget, hot dog, ppj, kid...........
If you let your server know that nothing is appealing to your son, they will try to accomodate you if possible. I have seen this happen at many, many restaurants at WDW.....happy eating!
My nephew went bonkers for the Uncrustables PB&J sandwiches readily available at Disney (try your resort Grab 'n Go area). You can always use a snack credit to keep one of those handy as "just in case" measure. I think they were about $2, so you may even pay OOP for this in case of emergency treat. You're a Mom, you know about these things. I'm just an auntie and am still in shock over my nephew's utter glee upon seeing those "gross" things.