What does the allergic to everything vegan eat?

I have been working at an organic food co-op at my university and some of our customers are vegan and have allergies, more than you mentioned such as being allergic to fructose which means they can't eat tomato and onion, some can't eat garlic either. We can make foods which do not contain those ingredients, we have a baker who makes gluten free vegan cakes using rice flower and almond meal. But yeah, anybody allergic to nuts, grains and legumes is going to have a hard time as a vegan. But if they made all their own food they could manage it.