I am not going to launch into a long list of ways to prepare today. Today just one idea: teach your child that it is perfectly acceptable to tell ANY adult in the building no. And to stand their ground. Let me explain.
I remember getting my daughter off of the bus one afternoon, shortly after she started kindergarten. She had her mouth slightly open, and her lips looked vaguely like she had spent the day in the Sahara. I thought it was just the beginning of cold weather chapping. No.
My daughter looked at me and said, through immobile lips, "Mommy, do you know why I'm not moving my mouth? Because I had to touch cheese today and I'm afraid that if it got on my hands and I touched my mouth, it could get in my mouth." My daughter had spent the afternoon in terror that she might have an allergic reaction.
I took her home, washed her hands and mouth, and listened to the whole story. Apparently there was a substitute teacher in class that day, and the lesson plan left for math class involved using goldfish crackers as a manipulative. When she told the teacher that she was allergic to the goldfish and should not have them, he told her she must participate. My daughter is very respectful and somewhat timid, so she did as she was instructed, even though it terrified her.
My first call was to the principal to let her know what had happened. The matter was, thankfully, addressed promptly and with the seriousness that it deserved.
My second course of action was to help my daughter understand that SHE IS ALLOWED TO SAY NO to any adult, anywhere, if it is to keep herself safe. As long as she does it politely. Further, I let her know it is fine to ask to speak to another adult about the situation. She can request to talk to the nurse or the principal, and she is allowed to leave the room and go do so without permission, provided she thinks it is to keep herself safe and she has politely advised the teacher of her intention.
Please make sure that your children know they are allowed to disagree with authority figures at school, and it is always ok to keep themselves safe. It is a valuable lesson that I overlooked initially. My daughter is now comfortable with this concept, and I know she will act appropriately.