I’m in kind of the same boat with my 7 year old. He’s a pretty picky eater already, so with the side-effect of curbing his appetite it was difficult to find something to take for school lunch. I’ve found giving him a divided container (not necessarily a Bento box, anything with the little compartments) with things like chopped up ham, a small handful of cashews and maybe some string cheese is something he will consistently eat. String cheese is debatable just because he likes to take the time to actually peel the strings, and sometimes runs out of time to finish the rest. But the general idea is small, snacky stuff seems to work best while anything resembling a “big” meal seems to put him off.