In reply to fergoid6:
Sorry for pointing out what might be blindingly obvious - but for best results make sure you're properly hydrated as well. This begins the night before (I would try and drink 1-1.5L of water before and after dinner), carries on before breakfast (a cup of water as soon as you wake up), during breakfast (don't drink too much tea or coffee, as it just makes you piss out all the water you've drunk and dehydrates you further) and all the way throughout the day. In my opinion - hydration is even more important than eating the right food (your body can run on no food for about 10 days, it cannot run on no water for more than 2 days).
A bit of salt in your hill food stops the water from passing right through your body - so personally I always try and take one salty snack for a long day (few cashews or peanuts usually).
The slower you're walking, the less that being hydrated is an issue (your heart beating slowly, and it meets a lot less resistance pumping thick blood around). The faster you walk, the faster your heart beats, and the more fluid resistance thick blood will create. So with that said, if you expect to be walking above your normal pace - pay extra attention to making sure you're hydrated.
Post edited at 12:55