E.A.
When my daughter's food allergies were at their worst (when she was <3yo) I focused on what she COULD eat rather than what she couldn't eat. She was allergic to all high Vitamin-C fruits (citrus, kiwi, cantaloupe, pineapple), milk, soy, eggs and MSG...anyway, I always had applesauce and apples around. I provided her with cups of allergen-free cereal, made lots of muffins to take on trips, cut up veggies, rice and almond milk, etc... Egg Replacer was a huge help when I baked. I made my own gravies. But again, I had to change the way I looked at it, not focus on what she *couldn't have* but what she *could* and made up my grocery list to include mostly fresh foods (not processed) and most of the family ate the way she ate (with a few exceptions).
With all that your kid can't eat, I would stay away from processed food as much as you can.
eta:
Her reactions were not life-threatening, she has eczema, and we were told her allergies would subside when she got older and they did. But I treated them very seriously and avoided those foods as if she would have had anaphylactic-type reactions.