I'm not sure about other schools but our school is fairly vigilant with allergies. We are a nut-free classroom as there is one (or more) student that is deathly allergic to nuts. Every start of the schoolyear, we are given the official notice that our classroom is nut-free due to allergies. Oh and our whole school is latex-free too so we get that notice as well.
When parents bring their homemade/pinterest treats, they make sure that it is nut-free. For those who know that there is a glutein and dairy sensitivity in the class too, they bring bday treats that are GFCF free too. During field trips, we are constantly reminded to keep lunches nut-free because there aren't necessarily designated seating spots for those who have said allergies.
IMO, those are reasonable accommodations. I have had to be more vigilant about the snacks that I send my child so yes, we of the allergy free world do adjust as well.
For those where all food is kept out of the classroom, are snacks eaten outside the classroom as well?