Hi greenbananas my DS is 5 and now in year 1 but I vividly remember feeling just like you are now before he started school. We have been very lucky in that the school have been fantastic about his allergies. My fear was that the staff would react in one of 2 ways, either not his allergies seriously enough (this was my greatest fear) or be so worried that they would be ringing me every time he had the slightest itch. Thankfully, neither of these happened.
The most important step for us was arranging a meeting with the Head, the class teacher, classroom assistant and school nurse to talk about his allergies. They took me very seriously and asked questions about what his reactions looked like so they knew what to look out for. I explained that he is touch allergic to some of his allergens and my concerns about milk time (in Wales, children still have free milk in schools) and lunch. They arranged for DS and a couple of other children who don't like milk to sit in a different area of the classroom at milk time. They are careful about wiping up any spills quickly. They also assigned one of the classroom assistants to keep an eye on him at lunchtime. He sits on the end of one of the tables next to one of his best friends who knows about his allergies and the assistant makes sure nobody gives him any food or touches his lunch etc. He even has school dinners once a week after a meeting with the dietician and canteen staff - he loves it (even though I was a nervous wreck the first few months!).
His medication is kept in the medical room in the school office but it is a very small school so there would never be a problem to get it quickly. If it was a much bigger site then I think I would want it to move around the school with him if poss or otherwise have 2 sets, one centrally and one in the classroom. All staff have epi-pen training on a regular basis and everyone in the school knows DS and his allergies (but as I said, it's a small school). His photo is on the board in the office and the canteen. He also wears his allergy strap every day.
Supply staff are given a folder containing details of any medical conditions in the class plus the classroom assistants inform them.
If the teacher is planning on doing an activity involving food, she speaks to me beforehand so that I can arrange alternative ingredients for DS. He is then able to join in safely (they do put him on a separate table to avoid cross contamination).
It is a very scary step but I did feel much better once I'd spoken to the staff. They reassured me that they were taking his allergies seriously and it was a good way of establishing communication links between us and the school. So far we haven't had any major reactions, just the odd case of hives/itching (which is normal for DS) where the school have given him Piriton, kept an eye on him and rung me to let me know. I haven't had to pick him up early at all as his reactions have all responded to Piriton.