After being seated, make sure to explain to the wait staff about your food allergy. Even though they have probably been trained to handle food allergies, explain your food allergy as if they know nothing. Be nice, and explain in simple terms about the severity of your food allergy, as if explaining to your elderly grandparents, or another child. The wait staff is often very patient, but also a bit hurried since they have other patrons. But it’s important, so make sure they fully understand.
And, when everything works out well, be sure to tip generously.