On a hot day, if you were walking 16+ miles, you probably would need to replenish some of your electrolytes. However, Gatorade would not be my first choice because it is loaded with HFCS and other preservatives.
Usually, I just drink plenty of water during regular workouts. However, some days I do like having a SOBE or Vitamin Water. Both use stevia instead of HFCS.
If you're looking for a general post workout drink to start repairing those muscle fibers, look no further than a pint of low fat chocolate milk. Chocolate milk has the right break down of carbs, fat and protein. You can read more about it here. there have been lots of studies showing how chocolate milk is a great all purpose post workout drink. www.fitnessmagazine.com/recipes/healthy-ea