hi - Noah has had gastro twice - the poor thing.. advice i got from gp was..
fluids - as the others have said - bfeeds small and regular and also gastrolyte - small amt often
the thing to watch for dehydration - damp nappy at least every 6 hrs etc etc as the others have said
in terms of food - some things he did recommend - potatoe - small amt often (i did mash) - make with no dairy or oil - literall just mashed potato. also apple is good as the pectin is a binder so helps with runny poo. i made some apple puree and mashed it into fresh steamed rice - this was good. stay away from high sugar items as they can make the poos worse... ( i was giving jelly for a while there... ooops!). stay away from dairy for 7 days or so after the last vomit. exception to this 'live' yoghurt - give this when she can handle it, it helps.
while he had the vomiting and diahorea i gave prob 8 'meals' of a couple of tsp and a small bfeed during the day and bfed one side only as often as poss in the nights (awful when they spew it all up again) and then as he got better i gradually increased the amts of BM each feed and then the food. i stayed away from dairy for about a week after the last vomit.
I also gave a probiotic and live yoghurt as soon as he could handle it after the 2nd bout and i think this helped ensure no recurrence. good luck!!! hope this info helps.