I think staying at the concert could partly depend on the circumstances surrounding it. In our school district all the kids have to take band in late elementary or early middle school for at least a year, I'm not sure exactly when. If it's a mandatory class than staying or even attending the concert should be optional if it's outside of the regular school day. If it's an optional class I can see extra requirements.
I don't know about middle or high school but our district is pretty smart about the younger kids, if they're doing a performance of any sort it's during the day and the parents are given a time for their child's grade. We don't have to sit through the other grades and they minimize parking issues.
We've been lucky so far with teachers, all of ours have been at least okay. I know that some parents are nightmares for the teachers, my cousin-in-law is like that. Last year they threw a fit because their kid's teachers were "mean" (my child's teacher said that they're strict but really nice) and had him moved. This year they've already thrown another fit because their kid was put with two male teachers and they'd heard that the bad kids get sent there, I don't know if they really get all the bad ones but what else would you call a kid that starts a fist fight in the hall in first grade? 
I'll raise a fit if something doesn't make sense but my kid knows better than to come home complaining about the teachers being mean if he was doing something wrong. Last year he was having trouble with a kid in gym so I talked to his teacher and she talked to the PE teacher, my child was dumb enough to make a snide comment about it in front of the teacher so he got in trouble too. 
funcakes - it sounds like you are very lucky! My kids go to a private school and there is no nurse. So any of the education on my children's allergies comes from me. All the medicine's are kept with the school's secretary. Thankfully she's a wonderful woman and I trust her whole-heartedly (sp?) to care for my children. Last year she had to give my son his breathing treatments as needed for asthma and she was wonderful. This year he can use an inhaler (yeah) and I know she'll take care of him just as well. She also has the epi-pen in her office in case of an allergic reaction and she had a son who needed an epi-pen so at least she knows what she's doing!!
Doug - I think you said that wonderfully! We have to teach our children responsibilty and being a team player is a big part of responsiblity.
well...anyways....my kids made it through the first week of snacks (supplied by teacher) and were able to eat what she brought in. I'm interested to see what the parents bring. I'm thinking about writing a note to the parents just explaining a little about the allergies and what can happen, thank them for thinking of my kids when making their snack choices, and also tell them if they are ever in doubt to please call me and to know that I will always be supplying a snack for my kids just in case. Do you think that would be an okay thing to do?
ABSOLUTELY!! When I had a peanut-allergic child in my class, his mother sent such a note to parents every year, and we didn't have a "bring snack for everyone" situation. She did it to request that no peanut snacks come to parties and to explain why he would say "No thank you" when snacks or birthday treats were sent in. It seemed to work well. She also came in and talked with the class each year about the allergy and why he had to stay away from anyone eating it.
My son's daycare is good about it-- if there is something in their kitchen they can't find a label for, they don't give it to him. They substitute some they know he can have or something from the box of snacks I send. They even keep cupcakes that I send in the freezer for when other kids bring birthday stuff. However, I am sure I'll be writing such letters when my son is in elementary school, though thankfully he will probably attend the one where I teach. I think most parents would appreciate it and anything we can do to politely and calmly spread awareness is helpful to all.
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