Hi my Son aged 6 is Dairy Free and has been since he was a baby (about 4 months) he is also allergic to eggs and nuts and has an epi-pen for all these allergies. His allergies are a way of life now, to be honest we don't really have to think about it, it comes naturally. here are some of the things's he can eat....
birds eye fish fingers... (in breadcrumbs not batter)
birds eye potato waffles,
cadbury's drinking chocolate in his soya milk... (believe it or not)
dolmio original bolognese ... ( i think the light one has dairy?)
any plain drum wheat pasta
Tesco's british butcher's choice pork sausages..
heinz spagetti hoops
walkers salt and vineger and plain crisps
I've just been throught the fridge and freezer, so hope this helps... (I know you said plain food)
Son is being allergy tested again in May... so wish us luck for then....
Rum Mum