If you have the regular stomach flu then it should go away within one week to two weeks and there's not all that much you can do to make it go away anytime sooner.
However you can help yourself feel better when you do have the stomach flu by changing what you eat and taking some Pepto Bismol and drinking things such as ginger, tea, clear broth, clear sodas, seltzer water etc.
And as for the food you should stick to the B.R.A.T diet which is known as Bananas, Rice, Applesauce and Toast.
Some other foods are chicken, soda crackers and other crackers and then gradually ease back into eating your normal foods.
Avoid any dairy products until the stomach virus is over with otherwise the dairy can upset your stomach more and could cause you to throw up.
If you do need to throw up though then do so because throwing up helps to get rid of bad things in your stomach and helps you feel much better.
If the stomach virus lasts longer than 10 to 14 days then you should see a doctor to make sure the virus isn't anymore serious than the normal stomach virus is.