I heard “be happy”‘s advice, and try drinking alot at least the day before. There are also 2 products we use that we feel help a lot:
1) Fastprin is sold by a lady in Chicago (maybe other places too) – it has a 12 hr time release for aspirin and tylenol (you take before the fast) and helps with caffeine and fasting headaches usually for the whole fast but if not then at least over half of the fast…
2) In Israel they sell a natural product called “tzom Kal” or “kalei tzom” (2 diff. brands) that you take before the fast after you’re done eating and while it doesn’t taste very good it helps keep you hydrated throughout the fast
Also, a rav once told me by yom kippur when I had extenuating circumstances) not to exert myself (even daven shmone esrei sitting as the chiyuv is more to fast for the kapara even than to daven) but also to keep cool (in strong air conditioning) and to wear in LOOSE clothing (I guess helps to keep cool? or less hunger? not sure but it helped…)
good luck & an easy and meaningful fast to every1!
may this be the the fast we ever have to do!