Two hours after vomiting and four hours after diarrhea you can attempt to drink clear liquids. Clear liquids can mean water, broth, popsicles or Gatorade. Because dehydration can be such a risk factor, even if you don't yet feel like having anything, you should try to take in liquids as best you can. If you vomit or have diarrhea again, wait two to four hours to let your system calm down. Do not, however, drink or eat any dairy products until you are a day or two out from your illness.
You will know when you are in the clear when you have that first feeling of actually being hungry. While your body needs food now that it can finally retain it, your mind is right to steer you away from steak dinners or macaroni and cheese. The first foods you should eat need to be bland, with natural sugars and carbohydrates. The best way to know what is safe to eat is to remember the BRAT diet: Bananas, Rice, Applesauce and Toast. While you can take a few liberties and use the BRAT diet as more of a guideline, don't overdo it or push your body farther than you can stomach.
While bananas and applesauce are pretty clear-cut, the rice portion of the diet can be in the form of dry Rice Chex, or rice cakes. As for the toast, while old wives' tales say burnt toast is best, it can also be modified: Try plain crackers like Ritz or Saltines, and pretzels at first. Once they have stayed down for a few hours, you can move up to chicken noodle soup or chicken and rice soup, adding both liquids and solids in one meal. For the next day you may still feel weak, and it is advisable to remain with the BRAT diet before you challenge your digestive system with anything substantial.