What to do with stomach flu?

Prevent dehydration. Lots of fluids, esp fluids with salts to prevent dehydration - either oral or IV if needed. Symptomatic management.
Hydrate & rest. Start w clear liquid like water, slightly flattened soda that is clear, or sports hydration drinks. Sip, sip, sip. Work up to solids w bland foods like bananas, rice, applesauce, toast, gelatin, or chicken. Avoid alcohol, nicotine, caffeine, dairy & high fat foods. Rest.