I've fasted for spiritual reasons for up to 14 days, I'm Christian.
Besides drinking more during the day, I changed my heavier meal to morning and my traditional breakfast foods were eaten at night.
As far as modest clothing, out here in our dry heat we always wear loose, light colored, long sleeved shirts. Some are button down, others are what might be called "peasant blouses" and have no fasteners. And some women whose religion and traditions dictate against wearing jeans or breeches, wear riding skirts.
I'd be interested to know what you find that works for you.