Miss Swede is also allergic to dairy, so we bring travel-sized rice milk cartons with us when we fly. Actually, with all of her allergies, we essentially have to bring all meals with us for the trip.
In the past, a doctor's note explaining her allergies, why she needs all of these food items, and what medicines we need to have on us has worked for us.
However, Mrs. Swede was travelling alone (LIH-LAX) with the kids right after Christmas, and TSA basically made them undergo secondary and teritary screenings to ensure the rice milk and foods weren't explosives.
It took 30 minutes.
In short, bring a detailed doctor's note, but also show up to the airport earlier than what you're used to.