Many moons ago, I assisted a guy who was trying to break a world record for the longest time underwater during a freshwater scuba dive... The record was around 6 days, so tank changes, warmth, food, water, sleep and bathroom breaks were each their own logistical challenge.
Anyways, we used camel packs for water and electrolytes, and his favorite method for consuming calories was to those little orange twist top gatorate bottles filled with protein shakes.
But I agree with what others said, for typical recreational diving, just hydrating a few hours prior to the dive and again immediately after is your best bet.