I haven't had the flu in years, but I do remember keeping regular ginger ale around for when you can't keep anything down. ginger also helps with nausea. here's some posts on the flu
https://forum.tudiabetes.org/topics/stomach-flu-and-type-1
https://forum.tudiabetes.org/topics/does-a-cold-or-the-flu-make-your-sugars-go-nuts