Everything?
At the very least the patient must be kept hydrated be it water or tea, juice, etc etc. At a minimum water because we don’t survive without water but we can go weeks without food.
You should get your doctors and a nutritionist involved ASAP.
You can also expect continued downhill overall health for days after treatments end and recovery is slower than most folks expect as well.
Other comments posted on this discussion have been informative as I read them.
Me personally I lived on Sprite, Jello and chicken broth for about three weeks.