No level of hydration seems to help
A frustrating symptom I have is being constantly dehydrated enough that my digestive system causes me a lot of grief, but also feeling sick whenever I drink enough water to do anything about the situation. This morning I got a decent amount of IV fluids, and I felt mostly normal for once.
From the comments
James Petrosky: Soft drinks are better on the stomach, but help the dehydration less.
Some chemo patients get IV fluids as part of their recovery. It would trap me in my apartment for more days per cycle, but I'm still going to ask about it.