I always found this hard and still do! Will do a list of our most common lunches, I'm not 100% sure how dairy/egg free they are though.
Dry pasta/pasta with cheese (you can get vegan cheese but it's a bit disgusting)
Fish fingers
Veggie fingers
Potato croquettes/smilies
Sandwiches - A likes cheese and mayo, he doesn't like ham but your A might, or chicken and pesto? Tomato?
Houmous and pitta bread (I usually give a substantial amount of help with this, and tear the pitta up and dunk it into the houmous... otherwise the mess is unbelievable and for lunch I frankly cannot be arsed with it!)
plus will usually give grapes/yoghurt (can you get dairy free yoghurt?) plus some other fruit depending on what's available, maybe a stick of cheese, sometimes a stick of babycorn. Today I chopped a spring onion into long chunks and gave it to him (going out of date today so I thought why not try!), he seemed to like it!!
Don't forget snacks too, we worked up to three meals a day and then added in snacks, usually just fruit and breadsticks.