Only pack, what you KNOW your child WILL eat.
Otherwise, a child will NOT eat, even if they are hungry.
I volunteered at my kids Preschool and school, all the time... and this is what I see at lunch time. All the time.
Some kids have the full on cute/fancy/variety buffet at lunch in cute boxes/totes... and the kid, will not eat. Because, they don't like it. Thus, they go hungry. Thus, they get tired/fussy later. Then they go home, all tired and fussy because they have an empty stomach and the parent wonders why the kid is so fussy. It is because, they have had nothing in their tummy, since breakfast or snack time. Low blood sugar.
Experiment at home, with foods. Not at school. Then once you know, your child likes something, THEN you can send it to school.
Also, per my son, he is very picky. He would only want the SAME thing (a sandwich)... every day. I explained to the Teachers. It was no big deal. The main thing is that the child eat and does have a lunch that they will eat.
At home, is where you experiment and can have the full food pyramid at home.