Whenever I have the stomach flu the symptoms of the stomach flu usually go away within 3 days but sometimes the stomach flu can last as long as 10 days depending on how severe the stomach flu is.
Most you can do for a stomach flu is to keep hydrated with plenty of fluids, get plenty of rest and eat what's known as the BRAT diet which consists of bland foods such as Bananas, Rice, Apple Sauce and Toast but any other Bland foods can be eaten as well when you have the stomach flu.
You should avoid dairy products or any spicy foods during the stomach flu.
Also you're contagious for up to 48 hours when the stomach flu first begins and after 48 hours you should no longer be contagious.