When I'm on vacation my stress is reduced to the point where my 'appetite' drops, and this is despite the fact that I'm increasing my exercise load enormously (surfing, hiking, etc...)

I've noticed that stress causes me mild stomach pain, which can register as hunger. It also causes dry mouth which registers as thirst. If you're satisfying that thirst with sugary drinks long term, then you're going to be in trouble.

There is also so much novelty and more interesting stuff going on while on vacation that I don't find myself poking through the fridge out of boredom.