We've only just got our first allergic kid that we've had since I started with DS2. Actually, the first since it reopened in January. He's strongly allergic to dairy, somewhat allergic to egg, and his mum is anxious about nuts (can't say I blame her!).
As to what they have, well, it's a different parent cooking every day, so it varies. Based on what we used to do, when we had a dairy-allergic child before, I suspect there will be quite a bit of humous involved.
In theory, the main carb is meant to change from day to day (bread, pasta, couscous, rice, potato/pastry - waaaay too much wheat I know, and I will change that!), but at the moment, we have no gas, so people just do whatever.
It's always vegetarian, it's not ready meals etc, and it's meant to be organic where possible.