When you have the flu you should avoid any foods or drinks containing sugar, milk or any meat.
When having the flu you should eat only bland foods such as rice apple sauce, toast etc are all good foods for when you have the flu.
I also eat those Ramen Noodles when having the flu which is easy for me to get down especially if I have a sore throat along with the flu.
Drinking warm decaf tea with honey is also good for both the flu and for treating the sore throat.
Avoid drinking coffee while you have the flu since it can dehydrate your body and when you have the flu you need to drink liquids that can hydrate your body such as tea, water, juice etc.