First, with stomach flu, you want to eat as little as possible, but you need to drink enough and maintain your electrolytes (minerals in your body) so that you do not become dehydrated. Your best bet is to stay on clear liquids. You can use Gatorade or Pedialyte to assure you are getting enough of the minerals, plus fluid, that you need. You can also drink diluted tea. Once you are keeping these fluids down, try adding Jello or other gelatin desserts and sorbet to your diet. If those stay down okay, add dry toast, crackers, or steamed rice. Sometimes a soft-boiled or poached egg is okay at this stage, also.
After light, soft and bland things stay down for a number of hours, you can begin to add in other items that don't upset your stomach. Things like vegetable or chicken noodle soup are good options.
Good luck. I hope you feel better soon!