First of all, don't pressure yourself into getting everything just right within the next few days. It's kinda hard at the beginning and many many mistakes and slip ups will happen. It helps to individualize your plan, make a list of things the child will eat and then find a suitable substitute. No sense introducing a food like say bagels if they were never interested in bagels before.
Milk will probably be the easiest as there's lots out there: soy, rice, potato, almond etc. The big "G" is the hardest here and instead of going all out and buying a bread maker, I found it easier to use the GF/CF free mixes out there and put them in muffin or small loaf pans and that way they're already for lunch or a school snack. You'll probably do alot of experimenting till you get the right food that they'll eat.