My rule of thumb after flying is that I owe myself 500cc of water for each hour of flight time, and that's after drinking carry on water and the complementary (soft) drinks: flying itself is severely dehydrating, and hauling luggage around may be light exercise but I'll usually end up sweating at some point in it.

Having two drinks on the flight just means another 500cc of water, but yeah, skip rehydration after flying and you're going to have a bad time. Add booze, it will be a worse time.