DD4's school is also peanut free, so we do soy butter & jelly sandwiches. Some kids don't like it, but our dd loves her SB&J! At first we just told her it was "special" peanut butter until she was used to it. Now she knows it's different & that she can't have PB at school because it can make some other kids very sick.
When she was 3, we sent alot of finger foods (lower mess factor) and alot of variety--half an SB&J cut into pieces, cut up fruit, dry cheerios, raisins, cheese, Puffin bars (a type of cereal bar), etc. Now we send V8 juice, yogurt, applesauce, leftovers, etc., as well. Occasionally we include a 100-calorie pack of pretzels or whole wheat crackers.