Note to self: do not move to Chicago. 
Or, if it's ever necessary, plan to homeschool. 
No, it's not the academic values, or the teacher quality, or the test scores.  It's nothing to do with the lovely folk who live there.  My problem with Chicago? 
Some schools have a mandatory "purchase lunch here" policy.  Of course, there is the standard "medical conditions are exempt" caveat. 
My questions:  How must the medical conditions be documented?  And what constitutes a worthy medical excuse?  Diabetes, food allergies, Celiac Disease...migraines?  IBS?  Lactose intolerance?  Kosher requirements?  Vegetarian or vegan choices?  Behavior issues?  Autism? 
If they require a simple doctor's note, they usually require it every single year.  And sometimes a new one midyear when some policy or another changes.  It sounds reasonable to get your medical professional to write out a note for you.  But doctors seem to HATE this policy.  They have better things to do than take a 15 minute appointment to write a note stating that a medical condition has not been outgrown and that the parents, not the school administrators who have never met your child, should decide what, exactly, can and can not pass your child's teeth. 
And then there's the simple fact that some medical conditions, like IBS, don't require one specific diet.  It's an ongoing balancing act...and one day's requirements may be completely counter to another day's.  Control over diet is critical to the overall health of someone with severe IBS or chronic digestive issues...and I guarantee that by High School; digestive concerns are the last thing any child wants to discuss over lunch. 
Which brings up my next concern.  If bagged lunches are banned, then anyone who brings a bagged lunch will be under scrutiny.  The third degree can come about whether they are the best of friends, mortal enemies or complete strangers.  Why did you bring a lunch?  Why are you exempt from the hard and fast rules?  What are you eating...Why are you different? 
It's hard enough to be different.  To be unique.  And now some schools insist that the unique individuals get a doctor to document their needs and then go around in obvious defiance of the school rule because they are exempt?  This sends the wrong message. 
I don't know about other kids with food allergies.  But mine wants to slip just under the radar.  She wants to bring enough chocolate chip cookies to share so that she isn't 'different'.  She wants to donate a normal fruit platter, or be in charge of the crackers, or offer safe snacks that taste and appear 'normal' to her friends and schoolmates.  She wants to be safe and cocooned in her food world...but she doesn't want anyone else to question it or tease her about it. 

I'm sure there are kids who don't really care where their lunch comes from, or what's in it, as long as it tastes good.  And parents who are happy to let the school make good decisions.  There are plenty of families not paying any attention to the ratio of doughnuts and chips and cookies to fresh produce consumed in the household.  But taking control by removing choice from consumers (You must purchase lunch here, no outside food in a school where children are required by a court of law to attend) doesn't solve anything. 

I say ban soda if you have to ban something (it makes a sticky mess when spilled, and the way it sprays after being shaken up in a backpack all day can make a custodian cry), provide plenty of healthy options at the school...and turn a blind eye to the 'junk food' as long as it isn't consumed during class hours.  Continue encouraging and teaching about good choices, start a garden (They won't be interested the first year, so give it 5 years) and eventually kids will start to make better and better choices.  They have to be the ones to choose in the long run, we have to trust them with their own health.  Which means, we start by trusting them with their own lunch.