What Lil Me said is what I would say.
I just wanted to add not to bring anything with nuts in it unless you are told by the teacher that it's ok. I know that if there is one child who is allergic to nuts, nobody else is allowed to bring food with nuts or nuts alone.
Definitely, extra clothing, especially pants. Bring rainboots and extra pair of shoes/socks. Some preschools request an "inside" shoe and an "outside" shoe. So, you might need to buy one just to keep in her preschool. Some preschools provide their own snacks and meals. Definitely, all preschools have their own supplies, ie books, paints, crayons, toys, etc.
Hope this helps.