This is common to happen with children.
Few things which can help are try packed food which should be healthy and which he use to have back home., soups, sweetened drinks, packed diary products, well cooked simple rice products, juices , boiled water, lots of rest and if vomiting/nausea continues then oral anti-emetics.
If he gets watery diarrhea
with fever then possibility of gastroenteritis
would be likely and he might need oral antibiotics
.In that case watch for dehydration
Most children settle in week or two.